Understanding the Hydrogen Evolution Reaction Kinetics of Electrodeposited Nickel‐Molybdenum in Acidic, Near‐Neutral, and Alkaline Conditions

Direct Electroplating Ruthenium Precursor on the Surface Oxidized Nickel Foam for Efficient and Stable Bifunctional Alkaline Water Electrolysis

Water electrolysis to produce hydrogen (H2) using renewable energy is one of the most promising candidates for realizing carbon neutrality, but its reaction kinetics is hindered by sluggish anodic oxygen evolution reaction (OER). Ruthenium (Ru) in its high-valence state (oxide) provides one of the most active OER sites and is less costly, but thermodynamically unstable. The strong interaction between Ru nanoparticles (NPs) and nickel hydroxide (Ni(OH)2) is leveraged to directly form Ru-Ni(OH)2 on the surface of a porous nickel foam (NF) electrode via spontaneous galvanic replacement reaction. The formation of Ru─O─Ni bonds at the interface of the Ru NPs and Ni(OH)2 (Ru-Ni(OH)2) on the surface oxidized NF significantly enhance stability of the Ru-Ni(OH)2/NF electrode. In addition to OER, the catalyst is active enough for the hydrogen evolution reaction (HER). As a result, it is able to deliver overpotentials of 228 and 15 mV to reach 10 mA cm-2 for OER and HER, respectively. An industry-scale evaluation using Ru-Ni(OH)2/NF as both OER and HER electrodes demonstrates a high current density of 1500 mA cm-2 (OER: 410 mV; HER: 240 mV), surpassing commercial RuO2 (OER: 600 mV) and Pt/C based performance (HER: 265 mV).

Electroreduction of Captured CO2 on Silver Catalysts: Influence of the Capture Agent and Proton Source

In the context of carbon reutilization, the direct electroreduction of captured CO2 (c-CO2RR) appears as an appealing approach since it avoids the energetically costly separation of CO2 from the capture agent. In this process, CO2 is directly reduced from its captured form. Here, we investigate the influence of the capture agent and proton source on that reaction from a combination of theory and experiment. Specifically, we consider methoxide-captured CO2, NH3-captured CO2, and bicarbonate on silver electrocatalysts. We show that the proton source plays a key role in the interplay of the chemistries for the electroreduction of protons, free CO2, and captured CO2. Our density functional theory calculations, including the influence of the potential, demonstrate that a proton source with smaller pKa improves the reactivity for c-CO2RR, but also increases the selectivity toward the hydrogen evolution reaction (HER) on silver surfaces. Since c-CO2RR requires an additional chemical protonation step, the influence of the proton source is stronger than that of the HER. However, c-CO2RR cannot compete with the HER on Ag, Experimentally, the dominant product observed is H2 with low amounts of CO being produced. Through a rotating cylinder electrode cell of well-defined mass-transport properties, we conclude that although methanol solvent exhibits a lower HER activity, HER remains dominant over c-CO2RR. Our work suggests that methoxide is a potential alternative capture agent to NH3 for direct reduction of captured CO2, though challenges in catalyst design, particularly in reducing the onset potential of c-CO2RR to surpass the HER, remain to be addressed.

Unlocking the Potential of High Entropy Alloys in Electrochemical Water Splitting: A Review

The global pursuit of sustainable energy is focused on producing hydrogen through electrocatalysis driven by renewable energy. Recently, High entropy alloys (HEAs) have taken the spotlight in electrolysis due to their intriguing cocktail effect, broad design space, customizable electronic structure, and entropy stabilization effect. The tunability and complexity of HEAs allow a diverse range of active sites, optimizing adsorption strength and activity for electrochemical water splitting. This review comprehensively covers contemporary advancements in synthesis technique, design framework, and physio-chemical evaluation approaches for HEA-based electrocatalysts. Additionally, it explores design principles and strategies aimed at optimizing the catalytic activity, stability, and effectiveness of HEAs in hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water splitting. Through an in-depth investigation of these aspects, the complexity inherent in constituent element interactions, reaction processes, and active sites associated with HEAs is aimed to unravel. Eventually, an outlook regarding challenges and impending difficulties and an outline of the future direction of HEA in electrocatalysis is provided. The thorough knowledge offered in this review will assist in formulating and designing catalysts based on HEAs for the next generation of electrochemistry-related applications.

Unlocking the Potential: Atomically Thin 2D Fluoritene from Exfoliated Fluorite Ore and Its Electrochemical Activity

Fluorite mineral holds significant importance because of its optoelectronic properties and wide range of applications. Here, we report the successful exfoliation of bulk fluorite ore (calcium fluoride, CaF2) crystals into atomically thin two-dimensional fluoritene (2D CaF2) using a highly scalable liquid-phase exfoliation method. The microscopic and spectroscopy characterizations show the formation of (111) plane-oriented 2D CaF2 sheets with exfoliation-induced material strain due to bond breaking, leading to the changes in lattice parameter. Its potential role in electrocatalysis is further explored for deeper insight, and a probable mechanism is also discussed. The 2D CaF2 with long-term stability shows overpotential values of 670 and 770 mV vs RHE for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, at 10 mA cm-2. Computational simulations demonstrate the unique "direct-indirect" band gap switching with odd and even numbers of layers. Current work offers new avenues for exploring the structural and electrochemical properties of 2D CaF2 and its potential applicability.

Single-Atomic Co-N4 Sites with CrCo Nanoparticles for Metal-Air Battery-Driven Hydrogen Evolution

Designing highly active and robust earth abundant trifunctional electrocatalysts for energy storage and conversion applications remain an enormous challenge. Herein, we report a trifunctional electrocatalyst (CrCo/CoN4@CNT-5), synthesized at low calcination temperature (550 °C), which consists of Co-N4 single atom and CrCo alloy nanoparticles and exhibits outstanding electrocatalytic performance for the hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reaction. The catalyst is able to deliver a current density of 10 mA cm-2 in an alkaline electrolytic cell at a very low cell voltage of ∼1.60 V. When the catalyst is equipped in a liquid rechargeable Zn-air battery, it endowed a high open-circuit voltage with excellent cycling durability and outperformed the commercial Pt/C+IrO2 catalytic system. Furthermore, the Zn-air battery powered self-driven water splitting system is displayed using CrCo/CoN4@CNT-5 as sole trifunctional catalyst, delivering a high H2 evolution rate of 168 μmol h-1. Theoretical calculations reveal synergistic interaction between Co-N4 active sites and CrCo nanoparticles, favoring the Gibbs free energy for H2 evolution. The presence of Cr not only enhances the H2O adsorption and dissociation but also tunes the electronic property of CrCo nanoparticles to provide optimized hydrogen binding capacity to Co-N4 sites, thus giving rise to accelerated H2 evolution kinetics. This work highlights the importance of the presence of small quantity of Cr in enhancing the electrocatalytic activity as well as robustness of single-atom catalyst and suggests the design of the multifunctional robust electrocatalysts for long-term H2 evolution application.

Decoupled supercapacitive electrolyzer for membrane-free water splitting

Green hydrogen production via water splitting is vital for decarbonization of hard-to-abate industries. Its integration with renewable energy sources remains to be a challenge, due to the susceptibility to hazardous gas mixture during electrolysis. Here, we report a hybrid membrane-free cell based on earth-abundant materials for decoupled hydrogen production in either acidic or alkaline medium. The design combines the electrocatalytic reactions of an electrolyzer with a capacitive storage mechanism, leading to spatial/temporal separation of hydrogen and oxygen gases. An energy efficiency of 69% lower heating value (48 kWh/kg) at 10 mA/cm2 (5 cm-by-5 cm cell) was achieved using cobalt-iron phosphide bifunctional catalyst with 99% faradaic efficiency at 100 mA/cm2. Stable operation over 20 hours in alkaline medium shows no apparent electrode degradation. Moreover, the cell voltage breakdown reveals that substantial improvements can be achieved by tunning the activity of the bifunctional catalyst and improving the electrodes conductivity. The cell design offers increased flexibility and robustness for hydrogen production.

Enhancing the Hydrogen Evolution Performance of Tungsten Diphosphide on Carbon Fiber through Ruthenium Modification

Hydrogen-based energy systems hold promise for sustainable development and carbon neutrality, minimizing environmental impact with electrolysis as the preferred fossil-fuel-free hydrogen generation method. Effective electrocatalysts are required to reduce energy consumption and improve kinetics, given the need for additional voltage (overpotential, η) despite the theoretical water splitting potential of 1.23 V. To date, platinum has been acknowledged as the most effective but expensive hydrogen evolution reaction (HER) catalyst. Hence, we introduce a cost-effective (∼2-fold cheaper) ruthenium-modified tungsten diphosphide (Ru/WP2) catalyst on carbon fiber for HER in ∼0.5 M H2SO4, with η ≈ 34 mV at -10 mA cm-2 which can be comparable (only ∼2-fold higher) to benchmark Pt/C (η ≈ 17 mV). The HER performance of WP2 can be enhanced through the modification of ruthenium, as indicated by the electrochemical characterizations. Considering the Tafel value of ∼40 ± 0.2 mV dec-1, it can be inferred that Ru/WP2 follows the Volmer-Heyrovsky reaction pathway for hydrogen generation. Furthermore, the Faradaic efficiency estimation indicates that Ru/WP2 demonstrates a minimal loss of electrons during the electrochemical reaction with an estimated value of ∼98.7 ± 1.4%. Therefore, this study could emphasize the potential of the Ru/WP2 electrode in advancing sustainable hydrogen production through water splitting.

Electrografting of Phenyl Phosphate Layers onto Glassy Carbon for Tuning Catalytic Activity toward the Hydrogen Evolution Reaction

In this study, we explored the surface modification of a glassy carbon electrode through the electrografting of 4-Aminophenyl phosphate, which features heteroatoms and ionic properties. The electrochemical grafting process involves reducing in situ-generated diazonium derivatives. The primary objective of this research was to immobilize organic layers and assess their electrochemical and surface properties. Subsequently, the generated surface serves as a template for the electrochemical growth of Pd and Co nanoparticles on functionalized electrodes. The electrocatalytic performances of these hybrid electrodes in driving the hydrogen evolution reaction were investigated. The obtained results indicate an enhancement in the electrocatalytic activity of the modified electrodes, where lower overpotential and higher stability were observed when the catalyst was electrodeposited onto the attached ionic layer. These findings highlight the synergistic effect between the attached phenyl phosphate moieties and electrocatalysts.

Strategically Designed Pd-Induced Changes in Alkaline Hydrogen Evolution Reaction and Oxygen Evolution Reaction Performances of Electrochemical Water Oxidation by the Galvanically Synthesized MoO2/MoO3 Composite Thin Film

Electrochemical water oxidation is believed to be an effective pathway to produce clean, carbon-free, and environmentally sustainable green energy. In this work, we report a simple, easy-to-construct, facile, low-cost, and single-step galvanic technique to synthesize a Pd-supported temperature-assisted MoOx thin film nanocomposite for effective water oxidation. The most suitable nanocomposite exhibits very low overpotential at 10 mA/cm2 with smaller Tafel slope values for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) processes in an alkaline medium. The formation of a metal oxide-metal junction accelerates the growth of more active sites, promoting induced electronic synergism at the MoOx-Pd interface. This endows higher electrical conductivity and faster electron transfer kinetics, thus accelerating the faster water dissociation reaction following the Tafel-Volmer mechanism to boost the HER process in an alkaline medium. The excellent electrochemical HER and OER performances of our electrocatalyst even supersede the accomplishments of the benchmark catalysts Pt/C and RuO2. Moreover, neither of these two catalysts demonstrates both catalytic reactions, i.e., HER and OER at the same time, which have been observed for our synthesized catalyst. Our findings illustrate the potential of a thin-film MoOx-Pd nanocomposite to be an exceedingly effective electrocatalyst developed by interface engineering strategies. This also provides insight into designing several other semiconductor composite catalysts using simple synthesis techniques for highly efficient HER/OER processes that could be alternatives to benchmark electrocatalysts for water electrolysis.

Uncovering Key Factors in Graphene Aerogel-Based Electrocatalysts for Sustainable Hydrogen Production: An Unsupervised Machine Learning Approach

The application of principal component analysis (PCA) as an unsupervised learning method has been used in uncovering correlations among diverse features of aerogel-based electrocatalysts. This analytical approach facilitates a comprehensive exploration of catalytic activity, revealing intricate relationships with various physical and electrochemical properties. The first two principal components (PCs), collectively capturing nearly 70% of the total variance, attested the reliability and efficacy of PCA in unveiling meaningful patterns. This study challenges the conventional understanding that a material's reactivity is solely dictated by the quantity of catalyst loaded. Instead, it unveils a complex perspective, highlighting that reactivity is intricately influenced by the material's overall design and structure. The PCA bi-plot uncovers correlations between pH and Tafel slope, suggesting an interdependence between these variables and providing valuable insights into the complex interactions among physical and electrochemical properties. Tafel slope stands to be positively correlated with PC1 and PC2, showing an evident positive correlation with the pH. These findings showed that the pH can have a positive correlation with the Tafel slope, however, it does not necessarily reflect a direct positive correlation with the overpotential. The impact of pH on current density (j)and Tafel slope underscores the importance of adjusting pH to lower overpotential effectively, enhancing catalytic activity. Surface area (from 30 to 533 m2 g-1) emerges as a key physical property, inclusively inverse correlation with overpotential, indicating its direct role in lowering overpotential and increasing catalytic activity. The introduction of PC3, in conjunction with PC1, enriches the analysis by revealing consistent trends despite a slightly lower variance (60%). This reinforces the robustness of PCA in delineating distinct characteristics of graphene aerogels, affirming their potential implications in diverse electrocatalytic applications. In summary, PCA proves to be a valuable tool for unraveling complex relationships within aerogel-based electrocatalysts, extending insights beyond catalytic sites to emphasize the broader spectrum of material properties. This approach enhances comprehension of dataset intricacies and holds promise for guiding the development of more effective and versatile electrocatalytic materials.

Synthesis of Silver Nanoparticles from Silver Closo-Dodecaborate Film for Enhanced Hydrogen Evolution

The icosahedral closo dodecaborate cluster [B12 H12 ]2- is gaining increasing interest due to its unique properties including the ease of functionalization, 3D aromaticity, and formation of metal salts with high ion conductivity. In this work, simple and effective preparation of silver closo dodecaborte (Ag2 B12 H12 ) films is reported by an electrochemical route. The size of the Ag2 B12 H12 particles in the films can be tuned from nanometers to micrometers by varying the electrochemical parameters. Ag nanoclusters with controllable sizes are successfully generated via electrochemical reduction reactions or thermal anneal of the Ag2 B12 H12 films. When tested for hydrogen evolution reaction (HER) in an acidic solution, the as-prepared Ag nanoparticles deliver a current density of 10 mA cm-2 at 376 mV overpotential. This research sheds light on a new synthesis of [B12 H12 ]2- based thin films, the generation of metal nano-powders, and their application in HER or other applications.

Organometal Halide Perovskite-Based Photoelectrochemical Module Systems for Scalable Unassisted Solar Water Splitting

Despite achievements in the remarkable photoelectrochemical (PEC) performance of photoelectrodes based on organometal halide perovskites (OHPs), the scaling up of small-scale OHP-based PEC systems to large-scale systems remains a great challenge for their practical application in solar water splitting. Significant resistive losses and intrinsic defects are major obstacles to the scaling up of OHP-based PEC systems, leading to the PEC performance degradation of large-scale OHP photoelectrodes. Herein, a scalable design of the OHP-based PEC systems by modularization of the optimized OHP photoelectrodes exhibiting a high solar-to-hydrogen conversion efficiency of 10.4% is suggested. As a proof-of-concept, the OHP-based PEC module achieves an optimal PEC performance by avoiding major obstacles in the scaling up of the OHP photoelectrodes. The constructed OHP module is composed of a total of 16 OHP photoelectrodes, and a photocurrent of 11.52 mA is achieved under natural sunlight without external bias. The successful operation of unassisted solar water splitting using the OHP module without external bias can provide insights into the design of scalable OHP-based PEC systems for future practical application and commercialization.

Influence of boron doping level and calcination temperature on hydrogen evolution reaction in acid medium of metal-free graphene aerogels

In this work, metal-free boron-doped graphene-based aerogels were successfully synthesized via a one-step autoclave assembly followed by freeze-drying and used as electrocatalysts for the hydrogen evolution reaction (HER) in acidic media. The synthesized reduced graphene oxide aerogels (rGOA) showed improved electrocatalytic activity by introducing boron and structural defects. The amount of boric acid used both as a dopant and reducing agent in the synthesis was optimized (boric acid/GO mass ratio = 17.5) to practically reach the crystallization limit of boric acid (boric acid/GO mass ratio = 20). It was observed that the higher the amount of boric acid added, the more boron was incorporated into the carbonaceous structure, improving the electrocatalytic activity of the final aerogel. Furthermore, calcination of the boron-doped electrocatalyst at 600 °C resulted in final aerogels with low oxygen content, moderate surface area, bimodal pore size distribution, and a high electrochemical active surface area. The final 3D graphene aerogel developed in this work, showed such outstanding electrocatalytic activity in HER as to replace noble metal-based electrocatalysts in the future.

Three-dimensional Ni foam supported NiCoO2@Co3O4 nanowire-on-nanosheet arrays with rich oxygen vacancies as superior bifunctional catalytic electrodes for overall water splitting

Earth abundant transition metal oxide (EATMO)-based bifunctional catalysts for overall water splitting are highly desirable, but their performance is far from satisfactory due to low intrinsic activities of EATMOs toward electrocatalysis of both oxygen and hydrogen evolution reactions and poor electron transfer and transport capabilities. A three-dimensional (3-D) Ni-foam-supported NiCoO2@Co3O4 nanowire-on-nanosheet heterostructured array with rich oxygen vacancies has been synthesized, showing OER activity superior to most reported catalysts and even much higher than Ru and Ir-based ones and HER activity among the highest reported for non-noble-metal-based catalysts. The excellent activities are ascribed to the highly dense, ultrathin nanowire arrays epitaxially grown on an interconnected layered nanosheet array greatly facilitating electron transfer and providing numerous electrochemically accessible active sites and the high content of oxygen vacancies on nanowires greatly promoting OER and HER. When adopted as bifunctional electrodes for overall water splitting, this heterostructure shows an overvoltage (at 10 mA cm-2) lower than most reported electrolyzers and high stability. This work not only creates a 3-D EATMO-based integrated heterostructure as a low-cost, highly efficient bifunctional catalytic electrode for water splitting, but also provides a novel strategy to use unique heteronanostructures with rich surface defects for synergistically enhancing electrocatalytic activities.

Moving beyond Ti2C3Tx MXene to Pt-Decorated TiO2@TiC Core-Shell via Pulsed Laser in Reshaping Modification for Accelerating Hydrogen Evolution Kinetics

Phase engineering of nanocatalysts on specific facets is critical not only for enhancing catalytic activity but also for intensely understanding the impact of facet-based phase engineering on electrocatalytic reactions. In this study, we successfully reshaped a two-dimensional (2D) MXene (Ti₃C₂T_x) obtained by etching Ti₃AlC₂ MAX via a pulsed laser irradiation in liquid (PLIL) process. We produced a TiO₂@TiC core-shell structure in spheres with sizes of 200-350 nm, and then ∼2 nm ultrasmall Pt NPs were decorated on the surface of the TiO₂@TiC core-shell using the single-step PLIL method. These advances allow for a significant increase in electrocatalytic hydrogen evolution reaction (HER) activity under visible light illumination. The effect of optimal Pt loading on PLIL time was identified, and the resulting Pt/TiO₂@TiC/Pt-5 min sample demonstrated outstanding electrochemical and photoelectrochemical performance. The photoelectrochemical HER activity over Pt/TiO₂@TiC/Pt-5 min catalyst exhibits a low overpotential of 48 mV at 10 mA/cm² and an ultralow Tafel slope of 54.03 mV/dec with excellent stability of over 50 h, which is hydrogen production activity even superior to that of the commercial Pt/C catalysts (55 mV, 62.45 mV/dec). This investigation not only serves as a potential for laser-dependent phase engineering but also provides a reliable strategy for the rational design and fabrication of highly effective nanocatalysts.

Inverse 'intra-lattice' charge transfer in nickel-molybdenum dual electrocatalysts regulated by under-coordinating the molybdenum center

The prevalence of intermetallic charge transfer is a marvel for fine-tuning the electronic structure of active centers in electrocatalysts. Although Pauling electronegativity is the primary deciding factor for the direction of charge transfer, we report an unorthodox intra-lattice 'inverse' charge transfer from Mo to Ni in two systems, Ni₇₃Mo alloy electrodeposited on Cu nanowires and NiMo-hydroxide (Ni : Mo = 5 : 1) on Ni foam. The inverse charge transfer deciphered by X-ray absorption fine structure studies and X-ray photoelectron spectroscopy has been understood by the Bader charge and projected density of state analyses. The undercoordinated Mo-center pushes the Mo 4d-orbitals close to the Fermi energy in the valence band region while Ni 3d-orbitals lie in the conduction band. Since electrons are donated from the electron-rich Mo-center to the electron-poor Ni-center, the inverse charge transfer effect navigates the Mo-center to become positively charged and vice versa. The reverse charge distribution in Ni₇₃Mo accelerates the electrochemical hydrogen evolution reaction in alkaline and acidic media with 0.35 and 0.07 s^-1 turnover frequency at -33 ± 10 and -54 ± 8 mV versus the reversible hydrogen electrode, respectively. The corresponding mass activities are 10.5 ± 2 and 2.9 ± 0.3 A g^-1 at 100, and 54 mV overpotential, respectively. Anodic potential oxidizes the Ni-center of NiMo-hydroxide for alkaline water oxidation with 0.43 O₂ s^-1 turnover frequency at 290 mV overpotential. This extremely durable homologous couple achieves water and urea splitting with cell voltages of 1.48 ± 0.02 and 1.32 ± 0.02 V, respectively, at 10 mA cm^-2.

Heterostructured mixed metal oxide electrocatalyst for the hydrogen evolution reaction

The hydrogen evolution reaction (HER) has attracted considerable attention lately because of the high energy density and environmental friendliness of hydrogen energy. However, lack of efficient electrocatalysts and high price hinder its wide application. Compared to a single-phase metal oxide catalyst, mixed metal oxide (MMO) electrocatalysts emerge as a potential HER catalyst, especially providing heterostructured interfaces that can efficiently overcome the activation barrier for the hydrogen evolution reaction. In this mini-review, several design strategies for the synergistic effect of the MMO catalyst on the HER are summarized. In particular, metal oxide/metal oxide and metal/metal oxide interfaces are explained with fundamental mechanistic insights. Finally, existing challenges and future perspectives for the HER are discussed.

New Insights into the Surfactant-Assisted Liquid-Phase Exfoliation of Bi2S3 for Electrocatalytic Applications

During water electrolysis, adding an electrocatalyst for the hydrogen evolution reaction (HER) is necessary to reduce the activation barrier and thus enhance the reaction rate. Metal chalcogenide-based 2D nanomaterials have been studied as an alternative to noble metal electrocatalysts because of their interesting electrocatalytic properties and low costs of production. However, the difficulty in improving the catalytic efficiency and industrializing the synthetic methods have become a problem in the potential application of these species in electrocatalysis. Liquid-phase exfoliation (LPE) is a low-cost and scalable technique for lab- and industrial-scale synthesis of 2D-material colloidal inks. In this work, we present, to the best of our knowledge, for the first time a systematic study on the surfactant-assisted LPE of bulk Bi2S3 crystalline powder to produce nanosheets (NSs). Different dispersing agents and LPE conditions have been tested in order to obtain colloidal low-dimensional Bi2S3 NSs in H2O at optimized concentrations. Eventually, colloidally stable layered nano-sized Bi2S3 suspensions can be produced with yields of up to ~12.5%. The thus obtained low-dimensional Bi2S3 is proven to be more active for HER than the bulk starting material, showing an overpotential of only 235 mV and an optimized Tafel slope of 125 mV/dec. Our results provide a facile top-down method to produce nano-sized Bi2S3 through a green approach and demonstrate that this material can have a good potential as electrocatalyst for HER.

Enhancing Hydrogen Evolution Reaction via Synergistic Interaction between the [Mo3S13]2- Cluster Co-Catalyst and WSe2 Photocathode

A thiomolybdate [Mo₃S₁₃]^2- nanocluster is a promising catalyst for hydrogen evolution reaction (HER) due to the high number of active edge sites. In this work, thiomolybdate cluster films are prepared by spin-coating of a (NH₄)₂Mo₃S₁₃ solution both on FTO glass substrates as hydrogen evolving electrodes and on highly 00.1-textured WSe₂ for photoelectrochemical water splitting. As an electrocatalyst, [Mo₃S₁₃]^2- clusters demonstrate a low overpotential of 220 mV at 10 mA cm^-2 in 0.5 M H₂SO₄ electrolyte (pH 0.3) and remain structurally stable during the electrochemical cycling as revealed by in situ Raman spectroscopy. Moreover, as a co-catalyst on WSe₂, [Mo₃S₁₃]^2- clusters enhance the photocurrent substantially by more than two orders of magnitude (from 0.02 to 2.8 mA cm^-2 at 0 V vs RHE). The synergistic interactions between the photoelectrode and catalyst, i.e., surface passivation and band bending modification by the [Mo₃S₁₃]^2- cluster film, promoted HER catalytic activity of [Mo₃S₁₃]^2- clusters influenced by the WSe₂ support, are revealed by intensity-modulated photocurrent spectroscopy and density functional theory calculations, respectively. The band alignment of the WSe₂/[Mo₃S₁₃]^2- heterojunction, which facilitates the electron injection, is determined by correlating UV-vis with photoelectron yield spectroscopy results.

A Single Source, Scalable Route for Direct Isolation of Earth-Abundant Nanometal Carbide Water-Splitting Electrocatalysts

Single-phase M_xCs (M = Fe, Co, and Ni) were prepared by solvothermal conversion of Prussian blue single source precursors. The single source precursor is prepared in water, and the conversion process is carried out in alkylamines at reaction temperatures above 200 °C. The reaction is scalable using a commercial source of Fe-PB. High-resolution transmission electron microscopy, X-ray photoelectron microscopy, and powder X-ray diffraction confirm that carbides have thin oxide termination but lack graphitic surfaces. Electrocatalytic activity reveals that Fe₃C and Co₂C are oxygen evolution reaction electrocatalysts, while Ni₃C is a bifunctional [OER and hydrogen evolution reaction (HER)] electrocatalyst.

One A3B Porphyrin Structure-Three Successful Applications

Porphyrins are versatile structures capable of acting in multiple ways. A mixed substituted A3B porphyrin, 5-(3-hydroxy-phenyl)-10,15,20-tris-(3-methoxy-phenyl)-porphyrin and its Pt(II) complex, were synthesised and fully characterised by 1H- and 13C-NMR, TLC, UV-Vis, FT-IR, fluorescence, AFM, TEM and SEM with EDX microscopy, both in organic solvents and in acidic mediums. The pure compounds were used, firstly, as sensitive materials for sensitive and selective optical and fluorescence detection of hydroquinone with the best results in the range 0.039-6.71 µM and a detection limit of 0.013 µM and, secondly, as corrosion inhibitors for carbon-steel (OL) in an acid medium giving a best performance of 88% in the case of coverings with Pt-porphyrin. Finally, the electrocatalytic activity for the hydrogen and oxygen evolution reactions (HER and OER) of the free-base and Pt-metalated A3B porphyrins was evaluated in strong alkaline and acidic electrolyte solutions. The best results were obtained for the electrode modified with the metalated porphyrin, drop-casted on a graphite substrate from an N,N-dimethylformamide solution. In the strong acidic medium, the electrode displayed an HER overpotential of 108 mV, at i = -10 mA/cm2 and a Tafel slope value of 205 mV/dec.

Ferroelectric Modulation of Surface Electronic States in BaTiO3 for Enhanced Hydrogen Evolution Activity

Ferroelectric nanomaterials offer the promise of switchable electronic properties at the surface, with implications for photo- and electrocatalysis. Studies to date on the effect of ferroelectric surfaces in electrocatalysis have been primarily limited to nanoparticle systems where complex interfaces arise. Here, we use MBE-grown epitaxial BaTiO₃ thin films with atomically sharp interfaces as model surfaces to demonstrate the effect of ferroelectric polarization on the electronic structure, intermediate binding energy, and electrochemical activity toward the hydrogen evolution reaction (HER). Surface spectroscopy and ab initio DFT+U calculations of the well-defined (001) surfaces indicate that an upward polarized surface reduces the work function relative to downward polarization and leads to a smaller HER barrier, in agreement with the higher activity observed experimentally. Employing ferroelectric polarization to create multiple adsorbate interactions over a single electrocatalytic surface, as demonstrated in this work, may offer new opportunities for nanoscale catalysis design beyond traditional descriptors.

Sulfur-Bridged Bonds Boost the Conversion Reaction of the Flexible Self-Supporting MnS@MXene@CNF Anode for High-Rate and Long-Life Lithium-Ion Batteries

Manganese sulfide (MnS) has been found to be a suitable electrode material for lithium-ion batteries (LIBs) owing to its considerable theoretical capacity, high electrochemical activity, and low discharge voltage platform, while its poor electrical conductivity and severe pulverization caused by volume expansion of the material limit its practical application. To improve the rate performance and cycle stability of MnS in LIBs, the structure-control strategy has been used to design and fabricate new anode materials. Herein, the MnS@MXene@CNF (MMC, CNFs means carbon nanofibers) electrode has been prepared by electrospinning and a subsequent high-temperature annealing process. The MMC electrode exhibits excellent cyclic stability with a capacity retention rate close to 100% after 1000 cycles at 1000 mA/g and an improved rate performance with a specific capacity up to 500 mAh/g at a high current density of 5000 mA/g, much higher than the 308 mAh/g of the MnS@CNF (MC) electrode. The elevated electrochemical performance of the MMC electrode not only benefits from the unique structure of MnS nanoparticles evenly dispersed in the well-designed flexible self-supporting three-dimensional (3D) CNF network but, more importantly, also benefits from the formation of sulfur-bridged Mn-S-C bonds at the MnS/MXene interface. The newly formed bonds between MnS and MXene nanosheets can stabilize the structure of MnS near the interfaces and provide a channel for fast charge transfer, which notably increase both the reversibility and the rate of the conversion reaction during the charge/discharge process. This work may pave a new path for designing stable and self-supporting anodes for high-performance LIBs.

Electrochemical deposition of nickel from aqueous electrolytic baths prepared by dissolution of metallic powder

A new method of preparation of aqueous electrolyte baths for electrochemical deposition of nickel targets for medical accelerators is presented. It starts with fast dissolution of metallic Ni powder in a HNO3-free solvent. Such obtained raw solution does not require additional treatment aimed to removal nitrates, such as the acid evaporation and Ni salt precipitation-dissolution. It is used directly for preparation of the nickel plating baths after dilution with water, setting up pH value and after possible addition of H3BO3. The pH of the baths ranges from alkaline to acidic. Deposition of 95% of ca. 50 mg of Ni dissolved in the bath takes ca. 3.5 h for the alkaline electrolyte while for the acidic solution it requires ca. 7 h. The Ni deposits obtained from the acidic bath are physically and chemically more stable and possess smoother and crack-free surfaces as compared to the coatings deposited from the alkaline bath. A method of estimation of concentration of H2O2 in the electrolytic bath is also proposed.

A Combined Chemical-Electrochemical Process to Capture CO2 and Produce Hydrogen and Electricity

Several carbon sequestration technologies have been proposed to utilize carbon dioxide (CO2) to produce energy and chemical compounds. However, feasible technologies have not been adopted due to the low efficiency conversion rate and high-energy requirements. Process intensification increases the process productivity and efficiency by combining chemical reactions and separation operations. In this work, we present a model of a chemical-electrochemical cyclical process that can capture carbon dioxide as a bicarbonate salt. The proposed process also produces hydrogen and electrical energy. Carbon capture is enhanced by the reaction at the cathode that displaces the equilibrium into bicarbonate production. Literature data show that the cyclic process can produce stable operation for long times by preserving ionic balance using a suitable ionic membrane that regulates ionic flows between the two half-cells. Numerical simulations have validated the proof of concept. The proposed process could serve as a novel CO2 sequestration technology while producing electrical energy and hydrogen.