Ruthenium anchored on carbon nanotube electrocatalyst for hydrogen production with enhanced Faradaic efficiency

Femtosecond laser synthesis of metastable PtRu/graphene electrocatalysts for efficient hydrogen evolution reaction in acidic and alkaline solutions

Facile synthesis of nanoalloys with atomic dispersity is an effective means to engineer highly efficient electrocatalysts by maximizing the exposure of catalytically active sites. However, such effort faces challenges in practice. One key issue is the thermodynamic-driven phase separation because of differences in redox potentials across different elements. Conventional wet chemistry methods often lack the rapid high-energy input required to non-selectively reduce precursors and mix elements with differing crystallographic parameters or phases, processes hindered by kinetic barriers. Here, we employ a femtosecond (fs) laser liquid ablation technique to synthesize defect-rich PtRu alloys on carbon supports without the application of external reducing agents or capping ligands. The extreme light field generated by fs lasers facilitates the rapid synthesis and stabilization of nanoalloy particles. The synthesized PtRu nanoparticles exhibited remarkable hydrogen evolution reaction (HER) activity in 1 M KOH and 0.5 M H2SO4, with overpotentials of 15.5 mV and 13.6 mV at 10 mA cm-2, respectively. In alkaline and acidic solutions, the mass activity of PtRu/graphene catalyst was 4.7 and 4.3 times that of commercial Pt/C catalysts, respectively. The electrolyte/electrode interfacial properties were investigated using in-situ attenuated total reflection surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS). It was found that alloying Pt with Ru activates water molecules and optimizes the interfacial water structure and hydrogen adsorption energy. Populated free water molecules at the electrolyte/electrode (PtRu/graphene) interface facilitate the transport of reaction intermediates. In-situ Raman spectroscopy reveals that Ru directly participates in the Volmer step, serving as the active site for water dissociation. Our study demonstrates the potential of using fs lasers for materials engineering and designing ligand-free metastable nanoalloys for various applications.

Temperature-Responsive Polymer Grafted Carbon Nanotubes for Active Control of Mineral Scaling

Scaling presents a major challenge in water treatment industries, reducing operational efficiency and shortening the service life of membranes and plumbing systems. Frequent membrane replacement imposes a substantial economic burden. Traditional scale removal methods, including physical cleaning and chemical treatments, often cause membrane damage, environmental hazards, and additional costs. To address these challenges, this study developed an antideposition, self-cleaning membrane structure for combating scaling in water treatment. The membrane features a poly(N-isopropylacrylamide) coating grafted onto carbon nanotube surfaces, providing dual functionalities: temperature responsiveness and high conductivity. These properties enable polymer motion and bubble generation on the membrane surface upon application of electrical current. The polymer movement effectively reduces deposition during operation, while the bubbles generated during water splitting reactions act as a natural cleaning mechanism. This approach offers a sustainable and efficient solution to scaling issues in water treatment systems.

A Self-Supported Coral-like Pt/SnO2/Nb2O5/Nb Electrode: A Bifunctional Electrocatalyst for Membrane-Free Green H2 Production via Coupling Ethanol Selective Electrooxidation

The production of green hydrogen via water electrolysis faces challenges due to the sluggish oxygen evolution reaction at the anode. In this study, we developed a self-supported bifunctional Pt/SnO2/Nb2O5/Nb electrocatalyst capable of coupling the hydrogen evolution reaction to the selective ethanol oxidation reaction (EOR) in an acidic medium. The catalyst demonstrated efficacy for the EOR, with an E onset of +130 mV versus SHE results in a peak current density of 8.97 mA cm-2. The bifunctional electrocatalyst exhibited a spontaneous and rapid increase in current for the HER, achieving an overpotential of -48 mV for a current density of 5 mA cm-2 and a Faradaic efficiency of 99.7%. This efficient coupling of the EOR with the HER reduces energy consumption for green hydrogen generation compared to traditional water splitting. With hydrogen being the sole gaseous product, the HER-EOR electrolysis system can operate effectively without a membrane, promising a more cost-effective, sustainable, and efficient green hydrogen production.

Bioinspired Ruthenium-Porphyrin Electrocatalysts with Atomic N4/N2 Proximal Sites for Efficient Proton-Coupled Electron Transfer in Water Electrolysis

Mimicking the proton-coupled electron transfer (PCET) pathways of natural enzymes, we engineer a porphyrin-based ruthenium coordination polymer (Ru-PCPN) with precisely positioned atomic-level N4/N2 proximal sites through molecular-scale coordination engineering. This bioinspired architecture establishes a dual-site relay mechanism where the Ru-N2 center accelerates water dissociation kinetics while the adjacent Ru-N4 site optimizes hydrogen recombination. Experimental and theoretical results reveal that the sub-nanometer-proximate N4/N2 sites function as proton donor-acceptor pairs, enabling directional proton transfer via PCET and synergistically enhancing water electrolysis. When integrated with carbon substrates, the Ru-PCPN@CB catalyst demonstrates exceptional hydrogen evolution performance in alkaline conditions, achieving a low overpotential at 10 mA cm-2 (42 mV, comparable to 44 mV of Pt/C), high mass activity and TOF of 9.02 A mg-1 and 4.73 s-1 (∼7.0 and 3.6 times of Pt/C), and good stability. This work establishes atomic-scale coordination proximity as a new paradigm for breaking scaling relationships in multistep electrocatalysis.

Platinum Nanoparticles on Metalloid Antimony Functionalized Graphitic Nanoplatelets for Enhanced Water Electrolysis

Platinum (Pt) nanoparticles are considered to be the most efficient catalyst for acidic hydrogen evolution reaction (HER). However, they are expensive and unstable, because of agglomeration and Ostwald ripening. It is critically necessary for developing a better catalytic support to stabilize the Pt nanoparticles at low loading amounts. One efficient route to improving both catalytic activity and durability is metal catalysts stably anchored on heteroatom functionalized carbon supports via their strong interactions. Nevertheless, the interactions between "metallic" catalysts and "nonmetallic" heteroatom functionalized carbon supports are still unsatisfactory. Here, "metalloid" antimony (Sb) functionalized graphitic nanoplatelets (SbGnP) are reported to stably anchor Pt nanoparticles. The resulting Pt@SbGnP catalyst shows a record high acidic HER performance, attributable to the unique nature of Sb functional groups on SbGnP. Unlike typical low-period nonmetallic heteroatoms on carbon supports, high-period metalloid Sb with various oxidation states of SbOx provided strong binding sites to stably anchor Pt nanoparticles, suppressing particle aggregation, and thus sustaining catalytic activity and stability.

CNT-Supported RuNi Composites Enable High Round-Trip Efficiency in Regenerative Fuel Cells

Regenerative fuel cells hold significant potential for efficient, large-scale energy storage by reversibly converting electrical energy into hydrogen and vice versa, making them essential for leveraging intermittent renewable energy sources. However, their practical implementation is hindered by the unsatisfactory efficiency. Addressing this challenge requires the development of cost-effective electrocatalysts. In this study, a carbon nanotube (CNT)-supported RuNi composite with low Ru loading is developed as an efficient and stable catalyst for alkaline hydrogen and oxygen electrocatalysis, including hydrogen evolution, oxygen evolution, hydrogen oxidation, and oxygen reduction reaction. Furthermore, a regenerative fuel cell using this catalyst composite is assembled and evaluated under practical relevant conditions. As anticipated, the system exhibits outstanding performance in both the electrolyzer and fuel cell modes. Specifically, it achieves a low cell voltage of 1.64 V to achieve a current density of 1 A cm- 2 for the electrolyzer mode and delivers a high output voltage of 0.52 V at the same current density in fuel cell mode, resulting in a round-trip efficiency (RTE) of 31.6% without further optimization. The multifunctionality, high activity, and impressive RTE resulted by using the RuNi catalyst composites underscore its potential as a single catalyst for regenerative fuel cells.

Enhance Water Electrolysis for Green Hydrogen Production with Material Engineering: A Review

Water electrolysis, a traditional and highly technology, is gaining significant attention due to the growing demand for renewable energy resources. It stands as a promising solution for energy conversion, offer substantial benefits in environmental protection and sustainable development efforts. The aim of this research is to provide a concise review of the current state-of-the-art in the field of water electrolysis, focusing on the principles of water splitting fundamental, recent advancements in catalytic materials, various advanced characterization methods and emerging electrolysis technology improvements. Moreover, the paper delves into the development trends of catalysts engineering for water electrolysis, providing insight on how to enhance the catalytic performance. With the advancement of technology and the reduction of costs, hydrogen production through water electrolysis is expected to assume a more significant role in future energy ecosystem. This paper not only synthesizes existing knowledge but also highlights emerging opportunities and potential advancements in this field, offering a clear roadmap for further research and innovation.

Platinum-Nickel Oxide Cluster-Cluster Heterostructure Enabling Fast Hydrogen Evolution for Anion Exchange Membrane Water Electrolyzers

Carbon black has been extensively employed as the support for noble metal catalysts for electrocatalysis applications. However, the nearly catalytic inertness and weak interaction with metal species of carbon black are two major obstacles that hinder the further improvement of the catalytic performance. Herein, we report a surface functionalization strategy by decorating transition metal oxide clusters on the commercial carbon black to offer specific catalytic activity and enhanced interaction with metal species. In the case of NiOx cluster-decorated carbon black, a strongly coupled cluster-cluster heterostructure consisting of Pt clusters and NiOx clusters (Pt-NiOx/C) is formed and delivers greatly enhanced alkaline hydrogen evolution kinetics. The NiOx clusters can not only accelerate the hydrogen evolution process as the co-catalyst, but also optimize the adsorption of H intermediates on Pt and stabilize the Pt clusters. Notably, the anion exchange membrane water electrolyzer with Pt-NiOx/C as the cathode catalyst (with a loading of only 50 μgPt cm-2) delivers the most competitive electrochemical performance reported to date, requiring only 1.90 V to reach a current density of 2 A cm-2. The results demonstrate the significance of surface functionalization of carbonaceous supports toward the development of advanced electrocatalysts.

Modulation of Hydrogen Desorption Capability of Ruthenium Nanoparticles via Electronic Metal-Support Interactions for Enhanced Hydrogen Production in Alkaline Seawater

The development of efficient and stable electrocatalysts for the hydrogen evolution reaction (HER) is essential for the realization of effective hydrogen production via seawater electrolysis. Herein, the study has developed a simple method that combines electrospinning with subsequent thermal shock technology to effectively disperse ruthenium nanoparticles onto highly conductive titanium carbide nanofibers (Ru@TiC). The electronic metal-support interactions (EMSI) resulted from charge redistribution at the interface between the Ru nanoparticles and the TiC support can optimize hydrogen desorption kinetics of Ru sites and induce the hydrogen spillover phenomenon, thereby improving hydrogen evolution. As a result, the Ru@TiC catalyst exhibits outstanding HER activity, requiring low overpotentials of only 65 mV in alkaline seawater at the current density of 100 mA cm-2. Meanwhile, Ru@TiC demonstrates excellent stability, maintaining consistent operation at 500 mA cm-2 for at least 250 hours. Additionally, an anion exchange membrane electrolyzer incorporating Ru@TiC operated continuously for over 500 hours at 200 mA cm-2 in alkaline seawater. This study highlights the significant potential of robust TiC supports in the fabrication of efficient and enduring electrocatalysts that enhance hydrogen production in complex seawater environments.

Cluster-Scale Multisite Interface Reinforces Ruthenium-Based Anode Catalysts for Alkaline Anion Exchange Membrane Fuel Cells

Ruthenium (Ru) is a more cost-effective alternative to platinum anode catalysts for alkaline anion-exchange membrane fuel cells (AEMFCs), but suffers from severe competitive adsorption of hydrogen (Had) and hydroxyl (OHad). To address this concern, a strongly coupled multisite electrocatalyst with highly active cluster-scale ruthenium-tungsten oxide (Ru-WOx) interface, which could eliminate the competitive adsorption phenomenon and achieve high coverage of OHad and Had at Ru and WOx domains, respectively, is designed. The experimental and theoretical results demonstrate that WOx domain functions as a proton sponge to perpetually accommodate the activated hydrogen species that spillover from the adjacent Ru domain, and the resulting WO-Had species are readily coupled with Ru-OHad at the heterointerface to finish the hydrogen oxidation reaction with faster kinetics via the thermodynamically favorable Tafel-Volmer mechanism. The AEMFC delivers a high peak power density of 1.36 W cm-2 with a low anode catalyst loading of 0.05 mgRu cm-2 and outstanding durability (negligible voltage decay over 80-h operation at 500 mA cm-2). This work offers completely new insights into understanding the alkaline HOR mechanism and designing advanced anode catalysts for AEMFCs.

Revealing the CO Tolerance Mechanism in Acidic Hydrogen Oxidation Reactions on Platinum-Based Catalyst Surfaces

The presence of trace CO impurity gas in hydrogen fuel can rapidly deactivate platinum-based hydrogen oxidation reaction (HOR) catalysts due to poisoning effects, yet the precise CO tolerance mechanism remains debated. Our designed Au@PtX bifunctional core-shell nanocatalysts exhibit excellent performance of CO tolerance in acidic solution during HOR and possess exceptional Raman spectroscopy enhancement. Through capturing and analyzing in situ Raman spectroscopy evidences on *OH, metal-O species and *CO evolution under 0.3 V, we confirm that oxygen-containing species on PtRu and PtSn catalysts promote the oxidation and desorption of *CO. While Ru enhances *CO adsorption on Pt, the primary CO tolerance performance of PtRu arises from *CO oxidation via a bifunctional pathway. Additionally, electronic structure of Sn reduces *CO adsorption on Pt sites, complementing the bifunctional mechanism to further enhance the CO tolerance performance of PtSn. These discoveries significantly deepen our understanding of the anti-poisoning mechanism of Pt-based catalysts in the HOR process and offer valuable insights for rational catalyst design.

Exploring the properties, types, and performance of atomic site catalysts in electrochemical hydrogen evolution reactions

Atomic site catalysts (ASCs) have recently gained prominence for their potential in the electrochemical hydrogen evolution reaction (HER) due to their exceptional activity, selectivity, and stability. ASCs with individual atoms dispersed on a support material, offer expanded surface areas and increased mass efficiency. This is because each atom in these catalysts serves as an active site, which enhances their catalytic activity. This review is focused on providing a detailed analysis of ASCs in the context of the HER. It will delve into their properties, types, and performance to provide a comprehensive understanding of their role in electrochemical HER processes. The introduction part underscores HER's significance in transitioning to sustainable energy sources and emphasizes the need for innovative catalysts like ASCs. The fundamentals of the HER section emphasizes the importance of understanding the HER and highlights the key role that catalysts play in HER. The review also explores the properties of ASCs with a specific emphasis on their atomic structure and categorizes the types based on their composition and structure. Within each category of ASCs, the review discusses their potential as catalysts for the HER. The performance section focuses on a thorough evaluation of ASCs in terms of their activity, selectivity, and stability in HER. The performance section assesses ASCs in terms of activity, selectivity, and stability, delving into reaction mechanisms via experimental and theoretical approaches, including density functional theory (DFT) studies. The review concludes by addressing ASC-related challenges in HER and proposing future research directions, aiming to inspire further innovation in sustainable catalysts for electrochemical HER.

Enhanced Alkaline Water Electrolysis by the Rational Decoration of RuOx with the In Situ-Grown CoFe Nanolayer

Rational engineering of the surfaces of heterogeneous catalysts (especially the surfaces of supported metals) can endow intriguing catalytic functionalities for electrochemical reactions. However, it often requires complicated steps, and even if it does not, breaking the trade-off between activity and stability is quite challenging. Herein, we present a strategy for reconstructing supported catalysts via in situ growth of metallic nanolayers from the perovskite oxide support. When Ru-coated LaFe0.9Co0.1O3 is thermally reduced, the CoFe nanoalloy spontaneously migrates onto the Ru and greatly increases the physicochemical stability of Ru in alkaline water electrolysis. Benefiting from an 81% reduction in Ru dissolution after decoration, it operates for over 200 h without noticeable degradation. Furthermore, the underlying Ru modifies the electronic structure and surface adsorption properties of the CoFe overlayer toward reaction intermediates, synergistically catalyzing both the oxygen evolution reaction and the hydrogen evolution reaction. Specifically, the mass activity of the oxygen evolution reaction is 64.1 times greater than that of commercial RuO2. Our work highlights a way to protect inherently unstable Ru from dissolution while allowing it to influence surface kinetics from the subsurface sites in heterogeneous catalysts.

Unveiling the Dual Active Sites of Ni/Co(OH)2-Ru Heterointerface for Robust Electrocatalytic Alkaline Seawater Splitting

Constructing bifunctional electrocatalysts through the synergistic effect of diverse metal sites is crucial for achieving high-efficiency and steady overall water splitting. Herein, a "dual-HER/OER-sites-in-one" strategy is proposed to regulate dominant active sites, wherein Ni/Co(OH)2-Ru heterogeneous catalysts formed on nickel foam (NF) demonstrate remarkable catalytic activity for oxygen evolution reaction (OER) as well as hydrogen evolution reaction (HER). Meanwhile, the potentials@10 mA cm-2 of Ni/Co(OH)2-Ru@NF for overall alkaline water and seawater splitting are only 1.36 and 1.41 V, respectively, surpassing those of commercial RuO2@NF and Pt/C@NF. The Ru site is identified as the primary active site for HER by density functional theory (DFT) calculations, while the Co(OH)2 site displays the minimal rate-determining step energy barrier (RDS) and functions as the main active site for OER. This study offers novel perspectives on the rational utilization of diverse metal species' catalytic capabilities for developing dual active sites multifunctional electrocatalysts.

Dominant Role of Coexisting Ruthenium Nanoclusters Over Single Atoms to Enhance Alkaline Hydrogen Evolution Reaction

Developing efficient and cost-effective electrocatalysts to replace expensive carbon-supported platinum nanoparticles for the alkaline hydrogen evolution reaction remains an important challenge. Recently, an innovative catalyst, composed of ruthenium single atoms (Ru1) integrated with small Ru nanoclusters (RuNC), has attracted considerable attention from the scientific community. However, because of its complexity, this catalyst remains a topic of some debate. Here, a method is reported of precisely controlling the ratios of Ru1 to RuNC on a nitrogenated carbon (NC)-based porous organic framework to produce Ru/NC catalysts, by using different amounts (0, 5, 10 wt.%) of reducing agent. The Ru/NC-10 catalyst, formed with 10 wt.% reducing agent, delivered the best performance under alkaline conditions, indicating that RuNC played a significant role in actual alkaline hydrogen evolution reaction (HER). An anion exchange membrane water electrolyzer (AEMWE) system using the Ru/NC-10 catalyst required a significantly lower operating voltage (1.72 V) than the commercial Pt/C catalyst (1.95 V) to achieve 500 mA cm-2. Moreover, the system can be operated at 100 mA cm-2 without notable performance decay for over 180 h. Theoretical calculations supported these experimental findings that Ru1 contributed to the water dissociation process, while RuNC is more actively associated with the hydrogen recombination process.

Cost-Effective RuNi Solid Solutions Prepared by Electrodeposition for Efficient Alkaline Hydrogen Evolution

The development of efficient hydrogen evolution reaction (HER) catalysts is crucial for water electrolysis. Currently, Ru-based catalysts are considered top contenders, but issues with stability, activity, and cost remain. In this work, RuNi alloys possessing a solid solution structure within the Ru lattice are prepared via straightforward electrodeposition on various substrates and assessed as HER catalysts in alkaline media. A RuNi solid solution containing 9.8 at. % Ni deposited on Ti substrate, wherein the Ni content greatly surpasses the solubility limit of Ni in Ru at room temperature, exhibits a considerably low overpotential of 28 mV at a current density of 10 mA cm- 2, along with good long-term stability (less than 100 mV increase in overpotential after 600 h). The enhancement in HER performance results from the increased electron density around Ru atoms due to Ni coordination, which facilitates the desorption of H* from the catalyst surface to produce H2. Concurrently, incorporating Ni reduces the Ru usage, rendering the RuNi alloy a viable cost-effective HER catalyst for practical applications.

Phosphorus doped few layer WS2 flakes grown by chemical vapor deposition for hydrogen evolution reactions

Water splitting is a promising pathway for hydrogen production, providing an environmentally friendly fuel source. More recently, great attention has been given to transition metal dichalcogenides (TMDCs) because of their interesting chemical and physical properties. In particular, tungsten disulfide (WS2) has garnered significant attention as a catalyst for this application due to its unique layered 2D structure. In this study, few-layered WS2 and phosphorus-doped WS2 (WS2/P) nanoflakes are synthesized on SiO2/Si substrates as electrocatalysts for hydrogen evolution reactions (HER) in acidic conditions. Analyses of the synthesized WS2 and WS2/P films reveal that the few-layered WS2 is of high quality, exhibiting continuity and uniformity. The presence of a strong peak in the photoluminescence spectrum confirms the mono/few layer nature of the synthesized samples. In additionally, scanning force microscopy in quantitative imaging mode reveals that the thinnest layers observed on the substrate have a height of 1.35 nm, indicating the presence of double-layer WS2. The WS2/P electrocatalyst demonstrates superior HER performance compared to pristine WS2, showing a low overpotential of 245 mV at 10 mA.cm-2 and a small Tafel slope of 123 mV.dec-1. Furthermore, WS2/P exhibits a greater electrochemical surface area and excellent catalytic stability under acidic conditions. Consequently, few layer phosphorus-doped WS2 proves to be a highly suitable electrocatalyst for hydrogen production compared to the WS2.

Enhancing Alkaline Hydrogen Evolution by Regulating H and OH Binding Strength through Strong Metal-Support Interactions

Establishing optimized metal-support interaction (MSI) between active sites and the substrate is essential for modulating the adsorption properties of key reaction intermediates during catalysis, thereby enhancing the catalytic performance. In this study, catalyst composites with varying degrees of MSI are constructed using ruthenium (Ru) and different carbon nanotubes, and their performance for alkaline hydrogen evolution reaction (HER) is systematically investigated. Detailed kinetic assessments reveal that catalysts with a strong MSI exhibit superior HER activity. For instance, Ru-O-CNT catalyst composite demonstrates an encouragingly low overpotential of 11 mV at 10 mA cm-2 and excellent stability. Electrochemical voltammetry analysis indicates that an effective MSI optimizes the binding strength of both *H and *OH, accelerating the HER process. Furthermore, we showcase that an industrial-level electrolyzer, assembled using Ru-O-CNT as the cathodic catalyst, achieves impressive performance with a low cell voltage of 1.72 V and high stability at a current density of 1 A cm-2.

Enhancing NiS performance: Na-doping for advanced photocatalytic and electrocatalytic applications

Alkali metal doping is a new and promising approach to enhance the photo/electrocatalytic activity of NiS-based catalyst systems. This work investigates the impact of sodium on the structural, electronic, and catalytic properties of NiS. Comprehensive characterization techniques demonstrate that Na-doping causes significant changes in the NiS lattice and surface chemistry translating into a larger bandgap than NiS. Photocatalytic experiments demonstrate 98.5% degradation of 2,4-DCP under visible light, attributing it to improved light absorption and charge separation by Na-NiS nanoparticles. The effect of pH and pKa on the degradation of 2,4-DCP has also been studied and reported. Additionally, electrochemical measurements of Na-NiS indicate overpotentials of 336 mV towards hydrogen evolution reaction (HER) and 350 mV towards oxygen evolution reaction (OER). The material's overall water splitting is found to be 2.61 V at a current density of 10 mA cm-2. The results highlight the potential of Na-NiS as a versatile catalyst for environmental remediation and clean energy applications, paving the way for further exploration and optimization of doped transition metal sulfides.

Elucidating Confinement and Microenvironment of Ru Clusters Stably Confined in MFI Zeolite for Efficient Propane Oxidation

Achieving active and stable heterogeneous catalysts by encapsulating noble metal species within zeolites is highly promising for high utilization and cost efficiency in thermal and environmental catalytic reactions. Ru, considered an economical noble metal alternative with comparable performance, faces great challenges within MFI-type microporous zeolites due to its high cohesive energy and mobility. Herein, an innovative strategy was explored that couples hydrothermal in situ ligand protection with stepwise calcination in a flowing atmosphere to embed ultrasmall Ru clusters anchored at K+-healed silanol sites (≡Si-Ruδ+-O-K complexes) within 10-membered ring sinusoidal channels of MFI. Comprehensive experiments and theoretical calculations unveiled that the interplay between confined Ru clusters and MFI induces local strain in MFI, creating a unique catalytic microenvironment around the Ru clusters. This synergy interaction enhances alkane deep oxidation as the confined Ru clusters and the MFI microenvironment collectively pre-activate C3H8 and O2, facilitate the cleavage of C-H and C-C bonds at low temperatures. Notably, the stable geometric and electronic properties of the confined Ru show exceptional thermal stability up to 1000 °C, rivaling fresh catalysts. These findings shed vital methodological and mechanistic insights for developing efficacious heterogeneous catalysts for thermal catalysis.

Heterogenization of molecular chalcoxides for electro-& photochemical H2 production

The endeavour to develop high-performance cost-effective catalytic systems with a minimal amount of active components and generation of hazardous waste is a significant and formidable step towards enhancing the hydrogen evolution reaction and the development of design principles with potential value in large scale applications. Here we investigate the heterogenization process of molecular chalcoxide catalysts and explore their electro- and photo-catalytic efficacy in driving the hydrogen evolution reaction (HER).

Deep eutectic Solvents-Assisted synthesis of NiFe-LDHs/Mo2Ti2C3: A bifunctional electrocatalyst for overall electrochemical water splitting in alkaline media

The development of efficient and stable electrocatalysts is crucial for the advancement of green and clean hydrogen energy technologies. In this work, we synthesized a nanocomposite of nickel-iron layered double hydroxide/molybdenum titanium carbide (NiFe-LDHs/Mo2Ti2C3) using a deep eutectic solvent (DESs) by the solvothermal method. The formation of NiFe-LDHs/Mo2Ti2C3 nanocomposite was confirmed by various electron microscopic and spectroscopic techniques. The synthesized nanocomposite was investigated as a bifunctional electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) under the alkaline condition. The NiFe-LDHs/Mo2Ti2C3-based electrodes exhibit small overpotentials of 204 and 306 mV for HER and OER at a current density of 10 mA cm-2. The anchor of NiFe-LDHs on the surface of Mo2Ti2C3 induces an interfacial synergistic effect, leading to a significantly improvement in electrochemical performance. Remarkably, the proposed NiFe-LDHs/Mo2Ti2C3 modified electrode demonstrates superior performance compared to many recently reported LDHs and MXenes-based electrocatalysts in an alkaline environment. Furthermore, a symmetrical two-electrode water splitting setup employing the NiFe-LDHs/Mo2Ti2C3 electrocatalyst requires an electrolysis voltage of 1.65 V to achieve a current density of 10 mA cm-2. The findings provide a new perspective on the rational design and synthesis of multifunctional electrocatalysts for electrochemical applications.

C60 Fullerene-Induced Reduction of Metal Ions: Synthesis of C60-Metal Cluster Heterostructures with High Electrocatalytic Hydrogen-Evolution Performance

Metal clusters, due to their small dimensions, contain a high proportion of surface atoms, thus possessing a significantly improved catalytic activity compared with their bulk counterparts and nanoparticles. Defective and modified carbon supports are effective in stabilizing metal clusters, however, the synthesis of isolated metal clusters still requires multiple steps and harsh conditions. Herein, we develop a C60 fullerene-driven spontaneous metal deposition process, where C60 serves as both a reductant and an anchor, to achieve uniform metal (Rh, Ir, Pt, Pd, Au and Ru) clusters without the need for any defects or functional groups on C60. Density functional theory calculations reveal that C60 possesses multiple strong metal adsorption sites, which favors stable and uniform deposition of metal atoms. In addition, owing to the electron-withdrawing properties of C60, the electronic structures of metal clusters are effectively regulated, not only optimizing the adsorption behavior of reaction intermediates but also accelerating the kinetics of hydrogen evolution reaction. The synthesized Ru/C60-300 exhibits remarkable performance for hydrogen evolution in an alkaline condition. This study demonstrates a facile and efficient method for synthesizing effective fullerene-supported metal cluster catalysts without any pretreatment and additional reducing agent.

Valence State and Catalytic Activity of Ni-Fe Oxide Embedded in Carbon Nanotube Catalysts

The catalytic activity of Ni-Fe oxide embedded in CNTs was investigated in terms of valence states and active oxygen species. Ni-Fe oxides were prepared by the sol-gel combustion process, and Ni-Fe oxides embedded in CNT catalysts were synthesized by the catalytic chemical vapor deposition (CCVD) method. The lattice structure of the Ni-Fe oxide catalysts was analyzed, and the lattice distortion was increased with the addition of Fe. The specific surface areas and pore structures of the Ni-Fe oxides embedded in CNTs were determined through the BET method. The nano-sized Ni-Fe oxides embedded in CNTs were observed using morphology analysis. The crystallinity and defects of CNTs were analyzed by Raman spectroscopy, and the ID/IG ratio of Ni1.25Fe0.75O/CNT was the lowest at 0.36, representing the high graphitization and low structural defects of the CNT surface. The valence states of Fe and Ni were changed by the interaction between catalysts and CNTs. The redox property of the catalysts was evaluated by H2-TPR analysis, and the H2 consumption of Ni1.25Fe0.75O/CNT was the highest at 2.764 mmol/g. The catalytic activity of Ni-Fe oxide embedded in CNT exhibited much higher activity than Ni-Fe oxide for the selective catalytic reduction of NOx with NH3 in the temperature range of 100 °C to 450 °C.

Phase Engineering-Mediated D-Band Center of Ru Sites Promote the Hydrogen Evolution Reaction Under Universal pH Condition

The rational design of pH-universal electrocatalyst with high-efficiency, low-cost and large current output suitable for industrial hydrogen evolution reaction (HER) is crucial for hydrogen production via water splitting. Herein, phase engineering of ruthenium (Ru) electrocatalyst comprised of metastable unconventional face-centered cubic (fcc) and conventional hexagonal close-packed (hcp) crystalline phase supported on nitrogen-doped carbon matrix (fcc/hcp-Ru/NC) is successfully synthesized through a facile pyrolysis approach. Fascinatingly, the fcc/hcp-Ru/NC displayed excellent electrocatalytic HER performance under a universal pH range. To deliver a current density of 10 mA cm-2, the fcc/hcp-Ru/NC required overpotentials of 16.8, 23.8 and 22.3 mV in 1 M KOH, 0.5 M H2SO4 and 1 M phosphate buffered solution (PBS), respectively. Even to drive an industrial-level current density of 500 and 1000 mA cm-2, the corresponding overpotentials are 189.8 and 284 mV in alkaline, 202 and 287 mV in acidic media, respectively. Experimental and theoretical calculation result unveiled that the charge migration from fcc-Ru to hcp-Ru induced by work function discrepancy within fcc/hcp-Ru/NC regulate the d-band center of Ru sites, which facilitated the water adsorption and dissociation, thus boosting the electrocatalytic HER performance. The present work paves the way for construction of novel and efficient electrocatalysts for energy conversion and storage.

Recent Developments in Membrane-Free Hybrid Water Electrolysis for Low-Cost Hydrogen Production Along with Value-Added Products

Water electrolysis using renewable energy is considered as a promising technique for sustainable and green hydrogen production. Conventional water electrolysis has two components - hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) occurring at the cathode and anode respectively. However, electrolysis of water suffers from high overpotential due to the slow kinetics of OER. To overcome this hybrid water electrolysis has been developed by replacing conventional anode oxidation producing oxygen with oxidation of cost-effective materials producing value-added chemicals. This review summarizes recent advances in organic oxidative reactions such as alcohols, urea, hydrazine, and biomass at the anode instead of OER. Furthermore, the review also highlights the use of membrane-free hybrid water electrolysis as a method to overcome the cost and complexity associated with conventional membrane-based electrolyzer thereby improving overall efficiency. This approach holds promise for scalable and cost-effective large-scale hydrogen production along with value-added products. Finally, current challenges and future perspectives are discussed for further development in membrane-free hybrid water electrolysis.

Ti3C2Tx MXene-supported ruthenium nanoclusters for efficient electrocatalytic hydrogen evolution

Developing an efficient and stable catalyst is both attractive and challenging for the electrochemical hydrogen evolution reaction (HER) due to the aggravation under the operating environment. MXene (Ti3C2Tx) is a potential catalyst support because of its abundant surface functional groups and unique hydrophilicity. However, anchoring noble metals onto MXene to construct high-performance electrocatalysts still presents some challenges. Herein, we present an MXene nanoparticle-supported Ru nanocluster (Ru@MXene-NP) electrocatalyst for HER. The Ru@MXene-NP not only effectively prohibits self-stacking but also ensures the full exposure of Ru nanoclusters. Thus, the Ru@MXene-NP catalyst exhibits an overpotential of 38.4 mV at 10 mA cm-2 and a Tafel slope of 26.4 mV dec-1 in an acidic medium, showcasing superior performance compared to most previously reported MXene-based catalysts. The small Tafel slope and low charge transfer resistance (Rct = 0.39 Ω) value indicate its fast electron transfer behavior. In addition, cyclic voltammetry curves and chronoamperometry tests demonstrate the high stability of Ru@MXene-NP. This work offers a novel perspective for designing catalysts by supporting noble metal nanoclusters on the MXene substrate's surface.

Dual-synergistic effect of medium-entropy metal sulfoselenide nanoparticles toward efficient overall seawater splitting

Developing efficient and durable electrodes for overall water splitting (OWS) in seawater electrolytes is a major challenge. Herein, we synthesized highly active and stable Fe1.2(CoNi)1.8S3Se3 medium-entropy metal sulfoselenide (MESSe) nanoparticles for the electrodes. The Fe1.2(CoNi)1.8S3Se3 MESSe electrode exhibited excellent electrocatalytic performance in alkaline simulated seawater, with a η100 value of 156 mV for the hydrogen evolution reaction and 262 mV for the oxygen evolution reaction. Compared to Fe1.2(CoNi)1.8S6 sulfide and Fe1.2(CoNi)1.8Se6 selenide, the electronic structure of Fe1.2(CoNi)1.8S3Se3 MESSe positively modulates the adsorption/desorption process of *H/*OH intermediate and significantly reduces the free energy of the rate-determining step, thereby accelerating the reaction kinetics of both hydrogen/oxygen evolution reactions. The performance of OWS is significantly enhanced by utilizing the prepared electrode, enabling it to achieve 100 mA cm-2 with only 1.77 V in alkaline simulated seawater. Furthermore, the durability of the electrode is maintained at this high current density in alkaline simulated seawater, alkaline seawater as well as seawater electrolyte. This work will lay the foundation for the development of innovative medium-entropy metal sulfoselenides, promoting their application in a wide range of electrochemical energy systems operating under extreme conditions.

Unlocking the Effects of the RuCo Alloy Ratio on Alkaline Hydrogen Production

Understanding the interaction between Ru and Co components and the alloy ratio effects on the catalytic process is a technical challenge that requires a precise alloy structural design. This study proposes an effective stepwise annealing method for the construction of RuCo alloy-based electrocatalysts with varied Ru:Co ratios. Interestingly, as the concentration of Co in the first-step pyrolysis products increases, the secondary pyrolysis results in RuCo composites undergoing a transition from incomplete alloying to alloy ratios of 1:1, 1:2, and 1:8. When the alloy ratio is 1:1, more Run+ and Co0 transform into Ru0 and Co2/3+. In 1 M KOH, RuCo-0.6/NC demonstrates outstanding catalytic performance and durability even superior to that of commercial Pt/C, delivering a lower overpotential of 16 mV at 10 mA cm-2. DFT calculations reveal that the fast H2O dissociation and moderate H adsorption guarantee the superior activity of RuCo.

Regulating Co-O covalency to manipulate mechanistic transformation for enhancing activity/durability in acidic water oxidation

Developing earth-abundant electrocatalysts with high activity and durability for acidic oxygen evolution reaction is essential for H2 production, yet it remains greatly challenging. Here, guided by theoretical calculations, the challenge of overcoming the balance between catalytic activity and dynamic durability for acidic OER in Co3O4 was effectively addressed via the preferential substitution of Ru for the Co2+ (Td) site of Co3O4. In situ characterization and DFT calculations show that the enhanced Co-O covalency after the introduction of Ru SAs facilitates the generation of OH* species and mitigates the unstable structure transformation via direct O-O coupling. The designed Ru SAs-CoO x catalyst (5.16 wt% Ru) exhibits enhanced OER activity (188 mV overpotential at 10 mA cm-2) and durability, outperforming most reported Co3O4-based and Ru-based electrocatalysts in acidic media.

Semi-Ionic F Modified N-Doped Porous Carbon Implanted with Ruthenium Nanoclusters toward Highly Efficient pH-Universal Hydrogen Generation

Developing high electroactivity ruthenium (Ru)-based electrocatalysts for pH-universal hydrogen evolution reaction (HER) is challenging due to the strong bonding strengths of key Ru─H/Ru─OH intermediates and sluggish water dissociation rates on active Ru sites. Herein, a semi-ionic F-modified N-doped porous carbon implanted with ruthenium nanoclusters (Ru/FNPC) is introduced by a hydrogel sealing-pyrolying-etching strategy toward highly efficient pH-universal hydrogen generation. Benefiting from the synergistic effects between Ru nanoclusters (Ru NCs) and hierarchically F, N-codoped porous carbon support, such synthesized catalyst displays exceptional HER reactivity and durability at all pH levels. The optimal 8Ru/FNPC affords ultralow overpotentials of 17.8, 71.2, and 53.8 mV at the current density of 10 mA cm-2 in alkaline, neutral, and acidic media, respectively. Density functional theory (DFT) calculations elucidate that the F-doped substrate to support Ru NCs weakens the adsorption energies of H and OH on Ru sites and reduces the energy barriers of elementary steps for HER, thus enhancing the intrinsic activity of Ru sites and accelerating the HER kinetics. This work provides new perspectives for the design of advanced electrocatalysts by porous carbon substrate implanted with ultrafine metal NCs for energy conversion applications.

Accelerating the Hydrogen Evolution Kinetics with a Pulsed Laser-Synthesized Platinum Nanocluster-Decorated Nitrogen-Doped Carbon Electrocatalyst for Alkaline Seawater Electrolysis

Efficient and durable electrocatalysts for the hydrogen evolution reaction (HER) in alkaline seawater environments are essential for sustainable hydrogen production. Zeolitic imidazolate framework-8 (ZIF-8) is synthesized through pulsed laser ablation in liquid, followed by pyrolysis, producing N-doped porous carbon (NC). NC matrix serves as a self-template, enabling Pt nanocluster decoration (NC-Pt) via pulsed laser irradiation in liquid. NC-Pt exhibits a large surface area, porous structure, high conductivity, N-rich carbon, abundant active sites, low Pt content, and a strong NC-Pt interaction. These properties enhance efficient mass transport during the HER. Remarkably, the optimized NC-Pt-4 catalyst achieves low HER overpotentials of 52, 57, and 53 mV to attain 10 mA cm-2 in alkaline, alkaline seawater, and simulated seawater, surpassing commercial Pt/C catalysts. In a two-electrode system with NC-Pt-4(-)ǀǀIrO2(+) as cathode and anode, it demonstrates excellent direct seawater electrolysis performance, with a low cell voltage of 1.63 mV to attain 10 mA cm-2 and remarkable stability. This study presents a rapid and efficient method for fabricating cost-effective and highly effective electrocatalysts for hydrogen production in alkaline and alkaline seawater environments.

One Stone, Three-Birds Approach: Ultra-active Ru/N, S-MoO2/CNTs Electrocatalyst for Overall Water Splitting in Wide Electrode Applications (NF, GC, and CC)

The construction of exceptionally multifunctional electrocatalysts is essential for various applications, but it poses significant challenges. A novel electrocatalyst, denoted as Ru/N, S-MoO2/CNTs, was successfully synthesized using a combination of mechano-grinding and hydrothermal/calcination techniques. The Ru/N, S-MoO2/CNTs demonstrates ultrasmall overpotentials of 12 and 163 mV in NF, 51 and 167 mV in GCE, and 54 and 173 mV in CC for HER and OER, respectively, at a current density of 10 mA/cm2 in alkaline medium. To accomplish electrocatalytic OWS, a current density of 10 mA/cm2 can be obtained by using a cell voltage of 1.446 V. Theoretical studies demonstrated that the inclusion of Ru, N, and S triggers a change in the composition of MoO2; produces oxygen vacancies; and forms Ru, N, and S-oxygen-Mo catalytic centers. The combination of Ru, N, and S nanoclusters; Ru, N, and S-oxygen-Mo catalytic centers; and OVs-enriched MoO2 would position it among the top electrocatalysts.

Terbium- and samarium-doped Li2ZrO3 perovskite materials as efficient and stable electrocatalysts for alkaline hydrogen evolution reactions

The preparation of highly active, rare earth, non-platinum-based catalysts for hydrogen evolution reactions (HER) in alkaline solutions would be useful in realizing green hydrogen production technology. Perovskite oxides are generally regarded as low-active HER catalysts, owing to their unsuitable hydrogen adsorption and water dissociation. In this article, we report on the synthesis of Li2ZrO3 perovskites substituted with samarium and terbium cations at A-sites for the HER. LSmZrO3 (LSmZO) and LTbZrO3 (LTbZO) perovskite oxides are more affordable materials, starting materials in abundance, environmentally friendly due to reduced usage of precious metal and moreover have potential for several sustainable synthesis methods compared to commercial Pt/C. The surface and elemental composition of the prepared materials have been confirmed by X-ray photoelectron spectroscopy (XPS). The morphology and composition analyses of the LSmZO and LTbZO catalysts showed spherical and regular particles, respectively. The electrochemical measurements were used to study the catalytic performance of the prepared catalyst for hydrogen evolution reactions in an alkaline solution. LTbZO generated 2.52 mmol/g/h hydrogen, whereas LSmZO produced 3.34 mmol/g/h hydrogen using chronoamperometry. This was supported by the fact that the HER electrocatalysts exhibited a Tafel slope of less than 120 mV/dec in a 1.0 M alkaline solution. A current density of 10 mA/cm2 is achieved at a potential of less than 505 mV. The hydrogen production rate of LTbZO was only 58.55%, whereas LSmZO had a higher Faradaic efficiency of 97.65%. The EIS results demonstrated that HER was highly beneficial to both electrocatalysts due to the relatively small charge transfer resistance and higher capacitance values.

Elucidating the effects of nitrogen and phosphorus co-doped carbon on complex spinel NiFe2O4 towards oxygen reduction reaction in alkaline media

The study presents for the first time complex spinel NiFe2O4 nanoparticles supported on nitrogen and phosphorus co-doped carbon nanosheets (NPCNS) prepared using sol gel and the carbonization of graphitic carbon nitride with lecithin as a highly active and durable electrocatalyst for oxygen reduction reaction. The physicochemical properties of complex spinel NiFe2O4 on NPCNS and subsequent nanomaterials were investigated using techniques such as X-ray diffraction, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The electrochemical activity of the electrocatalysts was evaluated using hydrodynamic linear sweep voltammetry, cyclic voltammetry, electrochemical impedance spectroscopy, and chronoamperometry. The electrocatalytic performance of the NiFe2O4/NPCNS nanohybrid electrocatalyst is dominated by the 4e- transfer mechanism, with an onset potential of 0.92 V vs. RHE, which is closer to that of the Pt/C, and a current density of 7.81 mA/cm2 that far exceeds that of the Pt/C. The nanohybrid demonstrated the best stability after 14 400 s, outstanding durability after 521 cycles, and the best ability to oxidize methanol and remove CO from its active sites during CO tolerance studies. This improved catalytic activity can be attributed to small nanoparticle sizes of the unique complex spinel nickel ferrite structure, N-Fe/Ni coordination of nanocomposite, high dispersion, substantial ECSA of 47.03 mF/cm2, and synergy caused by strong metal-support and electronic coupling interactions.

Oxophilic gallium single atoms bridged ruthenium clusters for practical anion-exchange membrane electrolyzer

The development of highly efficient and durable alkaline hydrogen evolution reaction (HER) catalysts is crucial for achieving high-performance practical anion exchange membrane water electrolyzer (AEMWE) at ampere-level current density. Herein, we report a design concept by employing Ga single atoms as an electronic bridge to stabilize the Ru clusters for boosting alkaline HER performance in practical AEMWE. Experimental and theoretical results collectively reveal that the bridged Ga sites trigger strong metal-support interaction for the homogeneous distribution of Ru clusters with high density, as well as optimize the Ru-H bond strength due to the electron transfer between Ru and Ga for enhanced intrinsic HER activity. Moreover, the oxophilic Ga sites near the Ru clusters tend to adsorb the hydroxyl species and accelerate the water dissociation for sufficient proton supplement in an alkaline medium. The Ru-GaSA/N-C catalyst exhibits a low overpotential of 4 ± 1 mV (10 mA cm-2) and high mass activity of 9.3 ± 0.5 A mg-1Ru at -0.05 V vs RHE. In particular, the Ru-GaSA/N-C-based AEMWE in 1 M KOH delivers a voltage of only 1.74 V to reach an industrial current density of 1 A cm-2, and can steadily operate at 1 A cm-2 for more than 170 h.

Constructing Directional Electrostatic Potential Difference via Gradient Nitrogen Doping for Efficient Oxygen Reduction Reaction

Nitrogen doping has been recognized as an important strategy to enhance the oxygen reduction reaction (ORR) activity of carbon-encapsulated transition metal catalysts (TM@C). However, previous reports on nitrogen doping have tended to result in a random distribution of nitrogen atoms, which leads to disordered electrostatic potential differences on the surface of carbon layers, limiting further control over the materials' electronic structure. Herein, a gradient nitrogen doping strategy to prepare nitrogen-deficient graphene and nitrogen-rich carbon nanotubes encapsulated cobalt nanoparticles catalysts (Co@CNTs@NG) is proposed. The unique gradient nitrogen doping leads to a gradual increase in the electrostatic potential of the carbon layer from the nitrogen-rich region to the nitrogen-deficient region, facilitating the directed electron transfer within these layers and ultimately optimizing the charge distribution of the material. Therefore, this strategy effectively regulates the density of state and work function of the material, further optimizing the adsorption of oxygen-containing intermediates and enhancing ORR activity. Theoretical and experimental results show that under controlled gradient nitrogen doping, Co@CNTs@NG exhibits significantly ORR performance (Eonset = 0.96 V, E1/2 = 0.86 V). At the same time, Co@CNTs@NG also displays excellent performance as a cathode material for Zn-air batteries, with peak power density of 132.65 mA cm-2 and open-circuit voltage (OCV) of 1.51 V. This work provides an effective gradient nitrogen doping strategy to optimize the ORR performance.

Designing core-shell heterostructure arrays based on snowflake NiCoFe-LTH shelled over W2N-WC nanowires as an advanced bi-functional electrocatalyst for boosting alkaline water/seawater electrolysis

The pursuit of efficient and sustainable hydrogen production through water splitting has led to intensive research in the field of electrocatalysis. However, the impediment posed by sluggish reaction kinetics has served as a significant barrier. This challenge has inspired the development of electrocatalysts characterized by high activity, abundance in earth's resources, and long-term stability. In addressing this obstacle, it is imperative to meticulously fine-tune the structure, morphology, and electronic state of electrocatalysts. By systematically manipulating these key parameters, the full potential of electrocatalysts can unleash, enhancing their catalytic activity and overall performance. Hence in this study, a novel heterostructure is designed, showcasing core-shell architectures achieved by covering W2N-WC nanowire arrays with tri-metallic Nickel-Cobalt-Iron layered triple hydroxide nanosheets on carbon felt support (NiCoFe-LTH/W2N-WC/CF). By integrating the different virtue such as binder free electrode design, synergistic effect between different components, core-shell structural advantages, high exposed active sites, high electrical conductivity and heterostructure design, NiCoFe-LTH/W2N-WC/CF demonstrates striking catalytic performances under alkaline conditions. The substantiation of all the mentioned advantages has been validated through electrochemical data in this study. According to these results NiCoFe-LTH/W2N-WC/CF achieves a current density of 10 mA cm-2 needs overpotential values of 101 mV for HER and 206 mV for OER, respectively. Moreover, as a bi-functional electrocatalyst for overall water splitting, a two-electrode device needs a voltage of 1.543 V and 1.569 V to reach a current density of 10 mA cm-2 for alkaline water and alkaline seawater electrolysis, respectively. Briefly, this research with attempting to combination of different factors try to present a promising stride towards advancing bi-functional catalytic activity with tailored architectures for practical green hydrogen production via electrochemical water splitting process.

Constructing Ru-O-TM Bridge in NiFe-LDH Enables High Current Hydrazine-assisted H2 Production

Hydrazine oxidation-assisted water splitting is a critical technology to tackle the high energy consumption in large-scale H2 production. Ru-based electrocatalysts hold promise for synergetic hydrogen reduction (HER) and hydrazine oxidation (HzOR) catalysis but are hindered by excessive superficial adsorption of reactant intermediate. Herein, this work designs Ru cluster anchoring on NiFe-LDH (denoted as Ruc/NiFe-LDH), which effectively enhances the intermediate adsorption capacity of Ru by constructing Ru─O─Ni/Fe bridges. Notably, it achieves an industrial current density of 1 A cm-2 at an unprecedentedly low voltage of 0.43 V, saving 3.94 kWh m-3 H2 in energy, and exhibits remarkable stability over 120 h at a high current density of 5 A cm-2. Advanced characterizations and theoretical calculation reveal that the presence of Ru─O─Ni/Fe bridges widens the d-band width (Wd) of the Ru cluster, leading to a lower d-band center and higher electron occupation on antibonding orbitals, thereby facilitating moderate adsorption energy and enhanced catalytic activity of Ru.

Electrochemically Induced Ru/CoOOH Synergistic Catalyst as Bifunctional Electrode Materials for Alkaline Overall Water Splitting

Efficient and affordable price bifunctional electrocatalysts based on transition metal oxides for oxygen and hydrogen evolution reactions have a balanced efficiency, but it remains a significant challenge to control their activity and durability. Herein, a trace Ru (0.74 wt.%) decorated ultrathin CoOOH nanosheets (≈4 nm) supported on the surface of nickel foam (Ru/CoOOH@NF) is rationally designed via an electrochemically induced strategy to effectively drive the electrolysis of alkaline overall water splitting. The as-synthesized Ru/CoOOH@NF electrocatalysts integrate the advantages of a large number of different HER (Ru nanoclusters) and OER (CoOOH nanosheets) active sites as well as strong in-suit structure stability, thereby exhibiting exceptional catalytic activity. In particular, the ultra-low overpotential of the HER (36 mV) and the OER (264 mV) are implemented to achieve 10 mA cm-2. Experimental and theoretical calculations also reveal that Ru/CoOOH@NF possesses high intrinsic conductivity, which facilitates electron release from H2O and H-OH bond breakage and accelerates electron/mass transfer by regulating the charge distribution. This work provides a new avenue for the rational design of low-cost and high-activity bifunctional electrocatalysts for large-scale water-splitting technology and expects to help contribute to the creation of various hybrid electrocatalysts.

Interfacial Design of Ti3C2Tx MXene/Graphene Heterostructures Boosted Ru Nanoclusters with High Activity Toward Hydrogen Evolution Reaction

The development of a cost-competitive and efficient electrocatalyst is both attractive and challenging for hydrogen production by hydrogen evolution reaction (HER). Herein, a facile glycol reduction method to construct Ru nanoclusters coupled with hierarchical exfoliated-MXene/reduced graphene oxide architectures (Ru-E-MXene/rGA) is reported. The hierarchical structure, formed by the self-assembly of graphene oxides, can effectively prohibit the self-stacking of MXene nanosheets. Meanwhile, the formation of the MXene/rGA interface can strongly trap the Ru3+ ions, resulting in the uniform distribution of Ru nanoclusters within Ru-E-MXene/rGA. The boosted catalytic activity and underlying catalytic mechanism during the HER process are proved by density functional theory. Ru-E-MXene/rGA exhibits overpotentials of 42 and 62 mV at 10 mA cm-2 in alkaline and acidic electrolytes, respectively. The small Tafel slope and charge transfer resistance (Rct) values elucidate its fast dynamic behavior. The cyclic voltammetry (CV) curves and chronoamperometry test confirm the high stability of Ru-E-MXene/rGA. These results demonstrate that coupling Ru nanoclusters with the MXene/rGA heterostructure represents an efficient strategy for constructing MXene-based catalysts with enhanced HER activity.

A self-supported porous NiMo electrocatalyst to boost the catalytic activity in the hydrogen evolution reaction

To develop hydrogen energy production and address the issues of global warming, inexpensive, effective, and long-lasting transition metal-based electrocatalysts for the synthesis of hydrogen are crucial. Herein, a porous electrocatalyst NiMo/Ni/NF was successfully constructed by a two-step electrodeposition process, and was used in the hydrogen evolution reaction (HER) of electrocatalytic water decomposition. NiMo nanoparticles were coated on porous Ni/NF grown on nickel foam (NF), leading to a resilient porous structure with enhanced conductivity for efficient charge transfer, as well as distinctive three-dimensional channels for quick electrolyte diffusion and gas release. Notably, the low overpotential (42 mV) and fast kinetics (Tafel slope of 44 mV dec-1) at a current density of 10 mA cm-2 in 1.0 M KOH solution demonstrate the excellent HER activity of the electrode, which was superior to that of recently reported non-noble metal-based catalysts. Additionally, NiMo/Ni/NF showed extraordinary catalytic durability in stability tests at a current density of 10 mA cm-2 for 70 h. The porous structure catalyst and the electrodeposition-electrocatalysis technique examined in this study offer new approaches for the advancement of the electrocatalysis field because of these benefits.

Scalable Design of Ru-Embedded Carbon Fabric Using Conventional Carbon Fiber Processing for Robust Electrocatalysts

Metal-carbon composites are extensively utilized as electrochemical catalysts but face critical challenges in mass production and stability. We report a scalable manufacturing process for ruthenium surface-embedded fabric electrocatalysts (Ru-SFECs) via conventional fiber/fabric manufacturing. Ru-SFECs have excellent catalytic activity and stability toward the hydrogen evolution reaction, exhibiting a low overpotential of 11.9 mV at a current density of 10 mA cm-2 in an alkaline solution (1.0 M aq KOH solution) with only a slight overpotential increment (6.5%) after 10,000 cycles, whereas under identical conditions, that of commercial Pt/C increases 6-fold (from 1.3 to 7.8 mV). Using semipilot-scale equipment, a protocol is optimized for fabricating continuous self-supported electrocatalytic electrodes. Tailoring the fiber processing parameters (tension and temperature) can optimize the structural development, thereby achieving good catalytic performance and mechanical integrity. These findings underscore the significance of self-supporting catalysts, offering a general framework for stable, binder-free electrocatalytic electrode design.

Transition metal-based electrocatalysts for alkaline overall water splitting: advancements, challenges, and perspectives

Water electrolysis is a promising method for efficiently producing hydrogen and oxygen, crucial for renewable energy conversion and fuel cell technologies. The hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are two key electrocatalytic reactions occurring during water splitting, necessitating the development of active, stable, and low-cost electrocatalysts. Transition metal (TM)-based electrocatalysts, spanning noble metals and TM oxides, phosphides, nitrides, carbides, borides, chalcogenides, and dichalcogenides, have garnered significant attention due to their outstanding characteristics, including high electronic conductivity, tunable valence electron configuration, high stability, and cost-effectiveness. This timely review discusses developments in TM-based electrocatalysts for the HER and OER in alkaline media in the last 10 years, revealing that the exposure of more accessible surface-active sites, specific electronic effects, and string effects are essential for the development of efficient electrocatalysts towards electrochemical water splitting application. This comprehensive review serves as a guide for designing and constructing state-of-the-art, high-performance bifunctional electrocatalysts based on TMs, particularly for applications in water splitting.

Ultrafine Ru nanoparticles stabilized by V8C7/C for enhanced hydrogen evolution reaction at all pH

The development of cost-effective electrocatalysts with high efficiency and long durability for hydrogen evolution reaction (HER) remains a great challenge in the field of water splitting. Herein, we design an ultrafine and highly dispersed Ru nanoparticles stabilized on porous V8C7/C matrix via pyrolysis of the metal-organic frameworks V-BDC (BDC: 1,4-benzenedicarboxylate). The obtained Ru-V8C7/C composite exhibits excellent HER performance in all pH ranges. At the overpotential of 40 mV, its mass activity is about 1.9, 4.1 and 9.4 times higher than that of commercial Pt/C in acidic, neutral and alkaline media, respectively. Meanwhile, Ru-V8C7/C shows the remarkably high stability in all pH ranges which, in particular, can maintain the current density of 10 mA cm-2 for over 150 h in 1.0 mol L-1 phosphate buffer saline (PBS). This outstanding HER performance can be attributed to the high intrinsic activity of Ru species and their strong interface interactions to the V8C7/C substrate. The synergistic effect of abundant active sites on the surface and the formed Ru-C-V units at the interface promotes the adsorption of reaction intermediates and the release of active sites, contributing the fast HER kinetics. This work provides a reference for developing versatile and robust HER catalysts by surface and interface regulation for pH tolerance.

Stable hydrogen evolution reaction at high current densities via designing the Ni single atoms and Ru nanoparticles linked by carbon bridges

Continuous and effective hydrogen evolution under high current densities remains a challenge for water electrolysis owing to the rapid performance degradation under continuous large-current operation. In this study, theoretical calculations, operando Raman spectroscopy, and CO stripping experiments confirm that Ru nanocrystals have a high resistance against deactivation because of the synergistic adsorption of OH intermediates (OHad) on the Ru and single atoms. Based on this conceptual model, we design the Ni single atoms modifying ultra-small Ru nanoparticle with defect carbon bridging structure (UP-RuNiSAs/C) via a unique unipolar pulse electrodeposition (UPED) strategy. As a result, the UP-RuNiSAs/C is found capable of running steadily for 100 h at 3 A cm-2, and shows a low overpotential of 9 mV at a current density of 10 mA cm-2 under alkaline conditions. Moreover, the UP-RuNiSAs/C allows an anion exchange membrane (AEM) electrolyzer to operate stably at 1.95 Vcell for 250 h at 1 A cm-2.

Uniformly dispersed ruthenium nanoparticles on porous carbon from coffee waste outperform platinum for hydrogen evolution reaction in alkaline media

Biowaste-derived carbon materials are a sustainable, environmentally friendly, and cost-effective way to create valuable materials. Activated carbon can be a supporting material for electrocatalysts because of its large specific surface area and porosity. However, activated carbon has low catalytic activity and needs to be functionalized with heteroatoms, metals, and combinations to improve conductivity and catalytic activity. Ruthenium (Ru) catalysts have great potential to replace bench market catalysts in hydrogen evolution reaction (HER) applications due to their similar hydrogen bond strength and relatively lower price. This study reports on the synthesis and characterizations of carbon-supported Ru catalysts with large surface areas (~ 1171 m2 g-1) derived from coffee waste. The uniformly dispersed Ru nanoparticles on the porous carbon has excellent electrocatalytic activity and outperformed the commercial catalyst platinum on carbon (Pt/C) toward the HER. As-synthesized catalyst needed only 27 mV to reach a current density of 10 mA cm-2, 58.4 mV dec-1 Tafel slope, and excellent long-term stability. Considering these results, the Ru nanoparticles on coffee waste-derived porous carbon can be utilized as excellent material that can replace platinum-based catalysts for the HER and contribute to the development of eco-friendly and low-cost electrocatalyst materials.

Metal Electrocatalysts for Hydrogen Production in Water Splitting

The rising demand for fossil fuels and the resulting pollution have raised environmental concerns about energy production. Undoubtedly, hydrogen is the best candidate for producing clean and sustainable energy now and in the future. Water splitting is a promising and efficient process for hydrogen production, where catalysts play a key role in the hydrogen evolution reaction (HER). HER electrocatalysis can be well performed by Pt with a low overpotential close to zero and a Tafel slope of about 30 mV dec-1. However, the main challenge in expanding the hydrogen production process is using efficient and inexpensive catalysts. Due to electrocatalytic activity and electrochemical stability, transition metal compounds are the best options for HER electrocatalysts. This study will focus on analyzing the current situation and recent advances in the design and development of nanostructured electrocatalysts for noble and non-noble metals in HER electrocatalysis. In general, strategies including doping, crystallization control, structural engineering, carbon nanomaterials, and increasing active sites by changing morphology are helpful to improve HER performance. Finally, the challenges and future perspectives in designing functional and stable electrocatalysts for HER in efficient hydrogen production from water-splitting electrolysis will be described.

Immobilizing Bimetallic RuCo Nanoalloys on Few-Layered MXene as a Robust Bifunctional Electrocatalyst for Overall Water Splitting

Doping Co atoms into Ru lattices can tune the electronic structure of active sites, and the conductive MXene can adjust the electrical conductivity of catalysts, which are both favorable for improving the electrocatalytic activity of the catalyst for water splitting. Here, ruthenium-cobalt bimetallic nanoalloys coupled with exfoliated Ti3 C2 Tx MXene (RuCo-Ti3 C2 Tx ) have been constructed by ice-templated and thermal activation. Due to the strong interaction between the RuCo nanoalloys and conductive MXene, RuCo-Ti3 C2 Tx not only exhibits an excellent hydrogen evolution reaction (HER) performance with a low overpotential and Tafel slope (60 mV, 34.8 mV dec-1 in 0.5 M H2 SO4 and 52 mV, 38.7 mV dec-1 in 1 M KOH), but also good oxygen evolution reaction (OER) performance in an alkaline electrolyte (266 mV, 111.1 mV dec-1 in 1 M KOH). The assembled RuCo-Ti3 C2 Tx ||RuCo-Ti3 C2 Tx electrolyzer requires a lower potential (1.56 V) than does the Pt/C||RuO2 electrolyzer at 10 mA cm-2 . A boosted catalytic HER activity from immobilizing the RuCo nanoalloys on MXene was unveiled by density functional theory calculations. This study provides a feasible and efficient strategy for developing MXene-based catalysts for overall water splitting.

Light-driven assembly of Pt clusters on Mo-NiOx nanosheets to achieve Pt/Mo-NiOx hybrid with dense heterointerfaces and optimized charge redistribution for alkaline hydrogen evolution

Designing cost-effective alkaline hydrogen evolution reaction (HER) catalysts with high water dissociation ability, enhanced hydroxyl transfer rate and optimized hydrogen adsorption free energy (ΔGH*) by a time and energy efficient strategy is pivotal, but still challenging for alkaline water electrolysis. Herein, Pt/Mo-NiOx hybrid consisting of Pt clusters assembled on Mo-doped NiOx nanosheet arrays is prepared on the surface of raw NiMo foam (NMF) by a light-driven strategy to address this challenge. Benefitting from the electronic interaction between Mo-NiOx and Pt, the Pt/Mo-NiOx composite owns optimized ΔGH* and is beneficial for accelerating water dissociation and hydroxyl transfer. As a result, the optimized Pt/Mo-NiOx/NMF electrode displays an exceptional alkaline HER activity with a low overpotential of 62 mV to obtain 100 mA cm-2 and a high Pt mass activity (13.2 times as high as that of commercial 20 wt% Pt/C). Furthermore, the assembled two-electrode cell of Pt/Mo-NiOx/NMF||NiFe-LDH/NF requires a voltage of only 1.549 V to deliver 100 mA cm-2, along with negligible activity decay after 70 h stability test. The present study provides a promising strategy for exploiting high-performance electrocatalysts towards alkaline HER.