Oxygen evolution reaction over catalytic single-site Co in a well-defined brookite TiO2 nanorod surface

Catalyst Design and Engineering for CO2-to-Formic Acid Electrosynthesis for a Low-Carbon Economy

Formic acid (FA) has emerged as a promising candidate for hydrogen energy storage due to its favorable properties such as low toxicity, low flammability, and high volumetric hydrogen storage capacity under ambient conditions. Recent analyses have suggested that FA produced by electrochemical carbon dioxide (CO2) reduction reaction (eCO2RR) using low-carbon electricity exhibits lower fugitive hydrogen (H2) emissions and global warming potential (GWP) during the H2 carrier production, storage and transportation processes compared to those of other alternatives like methanol, methylcyclohexane, and ammonia. eCO2RR to FA can enable industrially relevant current densities without the need for high pressures, high temperatures, or auxiliary hydrogen sources. However, the widespread implementation of eCO2RR to FA is hindered by the requirement for highly stable and selective catalysts. Herein, the aim is to explore and evaluate the potential of catalyst engineering in designing stable and selective nanostructured catalysts that can facilitate economically viable production of FA.

Ba2+-doping introduced piezoelectricity and efficient Ultrasound-Triggered bactericidal activity of brookite TiO2 nanorods

Exploring highly efficient ultrasound-triggered catalysts is pivotal for various areas. Herein, we presented that Ba2+ doped brookite TiO2 nanorod (TiO2: Ba) with polarization-induced charge separation is a candidate. The replacement of Ba2+ for Ti4+ not only induced significant lattice distortion to induce polarization but also created oxygen vacancy defects for facilitating the charge separation, leading to high-efficiency reactive oxygen species (ROS) evolution in the piezo-catalytic processes. Furthermore, the piezocatalytic ability to degrade dye wastewater demonstrates a rate constant of 0.172 min-1 and achieves a 100 % antibacterial rate at a low dose for eliminating E. coli. This study advances that doping can induce piezoelectricity and reveals that lattice distortion-induced polarization and vacancy defects engineering can improve ROS production, which might impact applications such as water disinfection and sonodynamic therapy.

Black titanium oxide: synthesis, modification, characterization, physiochemical properties, and emerging applications for energy conversion and storage, and environmental sustainability

Since its advent in 2011, black titanium oxide (B-TiOx) has garnered significant attention due to its exceptional optical characteristics, notably its enhanced absorption spectrum ranging from 200 to 2000 nm, in stark contrast to its unmodified counterpart. The escalating urgency to address global climate change has spurred intensified research into this material for sustainable hydrogen production through thermal, photocatalytic, electrocatalytic, or hybrid water-splitting techniques. The rapid advancements in this dynamic field necessitate a comprehensive update. In this review, we endeavor to provide a detailed examination and forward-looking insights into the captivating attributes, synthesis methods, modifications, and characterizations of B-TiOx, as well as a nuanced understanding of its physicochemical properties. We place particular emphasis on the potential integration of B-TiOx into solar and electrochemical energy systems, highlighting its applications in green hydrogen generation, CO2 reduction, and supercapacitor technology, among others. Recent breakthroughs in the structure-property relationship of B-TiOx and its applications, grounded in both theoretical and empirical studies, are underscored. Additionally, we will address the challenges of scaling up B-TiOx production, its long-term stability, and economic viability to align with ambitious future objectives.

Disentangling heterogeneous thermocatalytic formic acid dehydrogenation from an electrochemical perspective

Heterogeneous thermocatalysis of formic acid dehydrogenation by metals in solution is of great importance for chemical storage and production of hydrogen. Insightful understanding of the complicated formic acid dehydrogenation kinetics at the metal-solution interface is challenging and yet essential for the design of efficient heterogeneous formic acid dehydrogenation systems. In this work, formic acid dehydrogenation kinetics is initially studied from a perspective of electrochemistry by decoupling this reaction on Pd catalyst into two short-circuit half reactions, formic acid oxidation reaction and hydrogen evolution reaction and manipulating the electrical double layer impact from the solution side. The pH-dependences of formic acid dehydrogenation kinetics and the associated cation effect are attributed to the induced change of electric double layer structure and potential by means of electrochemical measurements involving kinetic isotope effect, in situ infrared spectroscopy as well as grand canonical quantum mechanics calculations. This work showcases how kinetic puzzles on some important heterogeneous catalytic reactions can be tackled by electrochemical theories and methodologies.

Evaluation of individual metal contribution on active sites tailoring in multimetallic oxygen evolution catalytic system

Synergistic effects among different metals have positioned multimetallic electrocatalysts as promising facilitators for enhancing the oxygen evolution reaction (OER), though understanding their precise mechanisms has remained elusive. Delving into the unique contributions of individual metals is crucial for comprehending the complex synergy within multimetallic systems. In this study, we employed quinary (Co, Ce, Fe, Cu, and Mn) molybdates as a model to systematically investigate the role of each metal species in tailoring active sites. Our systematic analyses unveiled the presence of crucial oxygen vacancies, which can be considered as the active sites in OER. Comparative analyses of the top-performing quinary molybdates and their quaternary counterparts highlighted distinct electronic interactions and varying densities of oxygen vacancies, indicative of the diverse electron and vacancy engineering capabilities inherent to different metals. Mott-schottky plots demonstrated the predominant contribution of Mn to specific catalytic activity, followed by Ce, Fe, Cu, and Co. Leveraging an in-situ methanol probing method, it was found that the introduction of Cu, Ce, Fe, and Mn weakened intermediate adsorption, with Mn and Ce having the most significant effects, whereas Co strengthened adsorption. This work can advance our comprehension of the role played by individual metals within multimetallic catalysts, thereby promoting a more profound understanding of synergistic effects.

Boosting the Electrochemical Oxygen Evolution with Nickel Oxide Nanoparticle-Modified Glassy Carbon Electrodes in Alkaline Solutions

The present work investigates the electrocatalysis of oxygen evolution (OE) on a glassy carbon electrode modified with nickel oxide nanoparticles (NPs) (nano-Ni) in an alkaline solution. The nano-Ni is electrodeposited from an acidic sulfate electrolyte containing various additives, such as glucose, glycerol, and dimethyl glyoxime. The NPs are characterized morphologically and electrochemically using scanning electron microscopy and cyclic voltammetry. The elemental composition and electronic state of the modified electrodes were analyzed using X-ray photoelectron spectroscopy. A considerable enhancement in electrocatalytic activity, depending on the additives used, is observed. The study also explores the effect of nickel oxide loading to optimize the process. The highest cathodic shift in the onset potential of the oxygen evolution reaction is achieved with nickel oxide deposited in the presence of ethylene glycol.

Lattice Oxygen Activation through Deep Oxidation of Co4N by Jahn-Teller-Active Dopants for Improved Electrocatalytic Oxygen Evolution

Triggering the lattice oxygen oxidation mechanism is crucial for improving oxygen evolution reaction (OER) performance, because it could bypass the scaling relation limitation associated with the conventional adsorbate evolution mechanism through the direct formation of oxygen-oxygen bond. High-valence transition metal sites are favorable for activating the lattice oxygen, but the deep oxidation of pre-catalysts suffers from a high thermodynamic barrier. Here, taking advantage of the Jahn-Teller (J-T) distortion induced structural instability, we incorporate high-spin Mn3+ (t 2 g 3 e g 1 ${{t}_{2g}^{3}{e}_{g}^{1}}$ ) dopant into Co4N. Mn dopants enable a surface structural transformation from Co4N to CoOOH, and finally to CoO2, as observed by various in situ spectroscopic investigations. Furthermore, the reconstructed surface on Mn-doped Co4N triggers the lattice oxygen activation, as evidenced experimentally by pH-dependent OER, tetramethylammonium cation adsorption and online electrochemical mass spectrometry measurements of 18O-labelled catalysts. In general, this work not only offers the introducing J-T effect approach to regulate the structural transition, but also provides an understanding about the influence of the catalyst's electronic configuration on determining the reaction route, which may inspire the design of more efficient catalysts with activated lattice oxygen.

Defect Engineering in Composition and Valence Band Center of Y2(YxRu1-x)2O7-δ Pyrochlore Electrocatalysts for Oxygen Evolution Reaction

Oxygen evolution reaction (OER) takes place in various types of electrochemical devices that are pivotal for the conversion and storage of renewable energy. This paper describes a strategy in the design of solid-state structures of OER electrocatalysts through controlling the cation substitution on the active metal site and consequently valence band center position of site-mixed Y2(YxRu1-x)2O7-δ pyrochlore to achieve high catalytic activity. We found that partially replacing the B-site Ru4+ cation with A-site Y3+ in pyrochlore-structured Y2Ru2O7-δ modifies the oxidation state of B-site Ru from 4+ to 5+, as observed by electron paramagnetic resonance (EPR) spectroscopy but does not continuously increase the oxygen vacancy concentration in these oxygen substoichiometric compositions, as quantified by thermogravimetric analysis (TGA) decomposition studies. We found the increased Ru oxidation state leads to a downshift in valence band center. X-ray photoelectron spectroscopy (XPS) analysis was performed to quantitatively determine the optimal band center to be ∼1.27 eV below the Fermi energy level based on the analysis of the valence band edge of these Ru-based Y2(YxRu1-x)2O7-δ OER electrocatalysts. This work highlights that defect engineering can be a practical, effective approach to the optimization of oxidation state and electronic band center for high OER catalytic performance in a quantitative manner.

Effective nitrogen doping of TiO2 polymorphs at mild temperatures for visible-light-responsive hydrogen evolution

Herein, a mild-temperature nitrogen doping route with the urea-derived gaseous species as the active doping agent is proposed to realize visible-light-responsive photocatalytic hydrogen evolution both for the anatase and rutile TiO2. DFT simulations reveal that the cyanic acid (HOCN), derived from the decomposition of urea, plays a curial role in the effective doping of nitrogen in TiO2 at mild temperatures. Photocatalytic performance demonstrates that both the anatase and rutile TiO2 doped at mild temperatures exhibit the highest hydrogen evolution rates, although the ones prepared at high temperatures possess higher absorbance in the visible range. Steady-state and transient surface photovoltage characterizations of these doped TiO2 polymorphs prepared at different temperatures reveal that harsh conditions (high temperature reaction) typically result in the formation of intrinsic defects that are detrimental to the transport of the low-energy visible-light-induced electrons, while the mild-temperature nitrogen-doping could flatten the pristine upward band bending without triggering the formation of Ti3+, thus achieving enhanced visible-light-responsive hydrogen evolution rates. We anticipate that our findings will provide inspiring information for shrinking the gap between the visible-light-absorbance and the visible-light-responsiveness in the band engineering of wide-bandgap metal-oxide photocatalysts.

Heterojunction-Induced Rapid Transformation of Ni3+/Ni2+ Sites which Mediates Urea Oxidation for Energy-Efficient Hydrogen Production

Water electrolysis is an environmentally-friendly strategy for hydrogen production but suffers from significant energy consumption. Substituting urea oxidation reaction (UOR) with lower theoretical voltage for water oxidation reaction adopting nickel-based electrocatalysts engenders reduced energy consumption for hydrogen production. The main obstacle remains strong interaction between accumulated Ni3+ and *COO in the conventional Ni3+-catalyzing pathway. Herein, a novel Ni3+/Ni2+ mediated pathway for UOR via constructing a heterojunction of nickel metaphosphate and nickel telluride (Ni2P4O12/NiTe), which efficiently lowers the energy barrier of UOR and avoids the accumulation of Ni3+ and excessive adsorption of *COO on the electrocatalysts, is developed. As a result, Ni2P4O12/NiTe demonstrates an exceptionally low potential of 1.313 V to achieve a current density of 10 mA cm-2 toward efficient urea oxidation reaction while simultaneously showcases an overpotential of merely 24 mV at 10 mA cm-2 for hydrogen evolution reaction. Constructing urea electrolysis electrolyzer using Ni2P4O12/NiTe at both sides attains 100 mA cm-2 at a low cell voltage of 1.475 V along with excellent stability over 500 h accompanied with nearly 100% Faradic efficiency.

Facet-Dependent Oxygen Evolution Reaction Activity of IrO2 from Quantum Mechanics and Experiments

The diversity of chemical environments present on unique crystallographic facets can drive dramatic differences in catalytic activity and the reaction mechanism. By coupling experimental investigations of five different IrO2 facets and theory, we characterize the detailed elemental steps of the surface redox processes and the rate-limiting processes for the oxygen evolution reaction (OER). The predicted complex evolution of surface adsorbates and the associated charge transfer as a function of applied potential matches well with the distinct redox features observed experimentally for the five facets. Our microkinetic model from grand canonical quantum mechanics (GC-QM) calculations demonstrates mechanistic differences between nucleophilic attack and O-O coupling across facets, providing the rates as a function of applied potential. These GC-QM calculations explain the higher OER activity observed on the (100), (001), and (110) facets and the lower activity observed for the (101) and (111) facets. This combined study with theory and experiment brings new insights into the structural features that either promote or hinder the OER activity of IrO2, which are expected to provide parallels in structural effects on other oxide surfaces.

Cobalt catalyzed ethane dehydrogenation to ethylene with CO2: Relationships between cobalt species and reaction pathways

TiO2, ZrO2 and a series of TiO2-ZrO2 (TxZ1, x means the atomic ratio of Ti/Zr = 10, 5, 1, 0.2 and 0.1) composite oxide supports were prepared through co-precipitation, and then 3 wt% Co was loaded through wetness impregnation methods. The obtained 3 wt% Co/TiO2 (3CT), 3 wt% Co/ZrO2 (3CZ) and 3 wt% Co/TxZ1 (3CTxZ1) catalysts were evaluated for the oxidative ethane dehydrogenation reaction with CO2 (CO2-ODHE) as a soft oxidant. 3CT1Z1 catalyst exhibits excellent catalytic properties, with C2H4 yield, C2H6 conversion and CO2 conversion about 24.5 %, 33.8 % and 18.0 % at 650 °C, respectively. X-Ray Diffraction (XRD), in-situ Raman, UV-vis diffuse reflectance spectra (UV-vis DRS), H2 temperature-programmed reduction (H2-TPR), Electron paramagnetic resonance (EPR) and quasi in-situ X-ray Photoelectron Spectroscopy (XPS) have been utilized to thoroughly characterize the investigated catalysts. The results revealed that 3CT1Z1 produced TiZrO4 solid solution with more metal defect sites and oxygen vacancies (Ov), promoting the formation of Co2+-TiZrO4 structure. Furthermore, the presence of Ov and Ti3+can facilitate the high dispersion and stabilization of Co2+, as well as suppressing the severe reduction of Co2+, leading to superior ethane oxidative dehydrogenation activity. Besides, less Co0 is beneficial to ODHE reaction, because of its promotion effects for reverse water gas shift reaction; however, more Co0 results in dry reforming reaction (DRE). This work will shed new lights for the design and preparation of highly efficient catalysts for ethylene production.

Coupling Curvature and Hydrophobicity: A Counterintuitive Strategy for Efficient Electroreduction of Nitrate into Ammonia

The electrochemical upcycling of nitrate (NO3-) to ammonia (NH3) holds promise for synergizing both wastewater treatment and NH3 synthesis. Efficient stripping of gaseous products (NH3, H2, and N2) from electrocatalysts is crucial for continuous and stable electrochemical reactions. This study evaluated a layered electrocatalyst structure using copper (Cu) dendrites to enable a high curvature and hydrophobicity and achieve a stratified liquid contact at the gas-liquid interface of the electrocatalyst layer. As such, gaseous product desorption or displacement from electrocatalysts was enhanced due to the separation of a wetted reaction zone and a nonwetted zone for gas transfer. Consequently, this electrocatalyst structure yielded a 2.9-fold boost in per-active-site activity compared with that with a low curvature and high hydrophilic counterpart. Moreover, a NH3 Faradaic efficiency of 90.9 ± 2.3% was achieved with nearly 100% NO3- conversion. This high-curvature hydrophobic Cu dendrite was further integrated with a gas-extraction membrane, which demonstrated a comparable NH3 yield from the real reverse osmosis retentate brine.

Activating nickel foam with trace titanium oxide for enhanced water oxidation

Nickel-based electrocatalysts for water oxidation suffer from low activity and poor stability. In this work, 0.015 mg cm-2 TiO2 nanosheets anchored on Ni foam addressed these problems after electrochemical activation. In situ investigations, including Raman spectra, corroborated the enhanced generation of highly active Ni(III)-O-O species on Ni foam in the presence of trace TiO2.

Water-Mediated Selectivity Control of CH3 OH versus CO/CH4 in CO2 Photoreduction on Single-Atom Implanted Nanotube Arrays

Controllable methanol production in artificial photosynthesis is highly desirable due to its high energy density and ease of storage. Herein, single atom Fe is implanted into TiO2 /SrTiO3 (TSr) nanotube arrays by two-step anodization and Sr-induced crystallization. The resulting Fe-TSr with both single Fe reduction centers and dominant oxidation facets (001) contributes to efficient CO2 photoreduction and water oxidation for controlled production of CH3 OH and CO/CH4 . The methanol yield can reach to 154.20 µmol gcat -1 h-1 with 98.90% selectivity by immersing all the catalyst in pure water, and the yield of CO/CH4 is 147.48 µmol gcat -1 h-1 with >99.99% selectivity when the catalyst completely outside water. This CH3 OH yield is 50 and 3 times higher than that of TiO2 and TSr and stands among all the state-of-the-art catalysts. The facile gas-solid and gas-liquid-solid phase switch can selectively control CH3 OH production from ≈0% (above H2 O) to 98.90% (in H2 O) via slowly immersing the catalyst into water, where abundant •OH and H2 O around Fe sites play important role in selective CH3 OH production. This work highlights a new insight for water-mediated CO2 photoreduction to controllably produce CH3 OH.

Building Block Metal Nanocluster-Based Growth in 1D Direction

Metal nanoclusters with precisely modulated structures at the nanoscale give us the opportunity to synthesize and investigate 1D nanomaterials at the atomic level. Herein, it realizes selective 1D growth of building block nanocluster "Au13 Cd2 " into three structurally different nanoclusters: "hand-in-hand" (Au13 Cd2 )2 O, "head-to-head" Au25 , and "shoulder-to-shoulder" Au33 . Detailed studies further reveals the growth mechanism and the growth-related tunable properties. This work provides new hints for the predictable structural transformation of nanoclusters and atomically precise construction of 1D nanomaterials.

Clearing Up Discrepancies in 2D and 3D Nickel Molybdate Hydrate Structures

When electrocatalysts are prepared, modification of the morphology is a common strategy to enhance their electrocatalytic performance. In this work, we have examined and characterized nanorods (3D) and nanosheets (2D) of nickel molybdate hydrates, which previously have been treated as the same material with just a variation in morphology. We thoroughly investigated the materials and report that they contain fundamentally different compounds with different crystal structures, chemical compositions, and chemical stabilities. The 3D nanorod structure exhibits the chemical formula NiMoO4·0.6H2O and crystallizes in a triclinic system, whereas the 2D nanosheet structures can be rationalized with Ni3MoO5-0.5x(OH)x·(2.3 - 0.5x)H2O, with a mixed valence of both Ni and Mo, which enables a layered crystal structure. The difference in structure and composition is supported by X-ray photoelectron spectroscopy, ion beam analysis, thermogravimetric analysis, X-ray diffraction, electron diffraction, infrared spectroscopy, Raman spectroscopy, and magnetic measurements. The previously proposed crystal structure for the nickel molybdate hydrate nanorods from the literature needs to be reconsidered and is here refined by ab initio molecular dynamics on a quantum mechanical level using density functional theory calculations to reproduce the experimental findings. Because the material is frequently studied as an electrocatalyst or catalyst precursor and both structures can appear in the same synthesis, a clear distinction between the two compounds is necessary to assess the underlying structure-to-function relationship and targeted electrocatalytic properties.

Hollow-Structured and Polyhedron-Shaped High Entropy Oxide toward Highly Active and Robust Oxygen Evolution Reaction in a Full pH Range

High entropy metal oxides (HEO) are superior to many reactions involving multi-step elementary reactions. However, controlled synthesis of hollow-structured HEO catalysts, which offers large surface area and fast mass transfer kinetics, remains challenging and unexplored due to the complicated metal precursors. Herein, a metal organic framework-templated synthesis of hollow-structured and polyhedron-shaped HEO catalysts assembled with ultra-small nanoparticles, with up to ten metal elements, can be achieved, by taking advantage of the ion-exchange method. ZnFeNiCuCoRu-O HEO catalyst displays excellent activity and ultra-stability for oxygen evolution reaction in full pH range, with an overpotential of 170 mV at a current density of 10 mA cm-2 , a Tafel slope of 56 mV dec-1 , and a decay of activity by 7% in 30 h in alkaline medium, as well as a 12% and 8% decay in acidic and neutral medium, respectively. DFT calculation indicates that the energy barrier of the potential determining step on Ru-Fe bridge site is significantly lower than any other Ru-related bridge sites for the unique hollow structured HEO structures. This work highlights the importance of ion-exchange method in preparing highly stable and active hollow-structured HEOs catalysts toward highly efficient energy conversion and storage devices.

Efficient and durable MoFeNi hydroxide anode: Room temperature recrystallization regulated morphology-, valence- and crystallinity-dependent water oxidation performance

The formation of crystal-amorphous (c-a) interfaces by modulating the crystallinity of the material is a promising strategy for the oxygen evolution reaction (OER). Herein, a recrystallization growth at room temperature to regulate the crystallinity of catalysts is reported. The MoFeNi hydroxide precursor was synthesized by the solvothermal method, and then the crystallinity of the material was controlled by adjusting the concentration of Na2S in the immersion solution. These c-a heterogeneous interfaces significantly improved the OER activity of the catalysts while ensuring structural stability. The best catalyst exhibited a low overpotential of 195 mV to reach 10 mA cm-2 in 1 M KOH. It also showed good stability, operating stably at high current densities for 96 h without significant degradation. In addition, the anode of the two-electrode water splitting electrolyzer required only 1.46 V to reach 10 mA cm-2 and operated for a long time without significant degradation. This method will provide new insights and perspectives for developing efficient and stable OER catalysts.

The concerted proton-electron transfer mechanism of proton migration in the electrochemical interface

The proton migration in the electrochemical interface is a fundamental electrochemical processes in proton involved reactions. We find fractional electron transfer, which is inversely proportional to the distance between the proton and electrode, during the proton migration under constant potential. The electrical energy carried by the transferred charge facilitates the proton to overcome the chemical barrier in the migration pathway, which is accounting for more than half electrical energy in the proton involved reactions. Consequently, less charge transfer and energy exchange take place in the reduction process. Therefore, the proton migration in the electrochemical interface is an essential component of the electrochemical reaction in terms of electron transfer and energy conversation, and are worthy of more attention in the rational design and optimization of electrochemical systems.

First-Row Transition Metals for Catalyzing Oxygen Redox

Rechargeable zinc-air batteries are widely recognized as a highly promising technology for energy conversion and storage, offering a cost-effective and viable alternative to commercial lithium-ion batteries due to their unique advantages. However, the practical application and commercialization of zinc-air batteries are hindered by the sluggish kinetics of the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Recently, extensive research has focused on the potential of first-row transition metals (Mn, Fe, Co, Ni, and Cu) as promising alternatives to noble metals in bifunctional ORR/OER electrocatalysts, leveraging their high-efficiency electrocatalytic activity and excellent durability. This review provides a comprehensive summary of the recent advancements in the mechanisms of ORR/OER, the performance of bifunctional electrocatalysts, and the preparation strategies employed for electrocatalysts based on first-row transition metals in alkaline media for zinc-air batteries. The paper concludes by proposing several challenges and highlighting emerging research trends for the future development of bifunctional electrocatalysts based on first-row transition metals.

Low-Voltage Hydrogen Production via Hydrogen Peroxide Oxidation Facilitated by Oxo Ligand Axially Coordinated to Cobalt in Phthalocyanine Moiety

A cobalt phthalocyanine having an electron-poor CoN4 (+δ) in its phthalocyanine moiety was presented as an electrocatalyst for hydrogen peroxide oxidation reaction (HPOR). We suggested that hydrogen peroxide as an electrolysis medium for hydrogen production and therefore as a hydrogen carrier, demonstrating that the electrocatalyst guaranteed high hydrogen production rate by hydrogen peroxide splitting. The electron deficiency of cobalt allows CoN4 to have the highly HPOR-active monovalent oxidation state and facilitates HPOR at small overpotentials range around the onset potential. The strong interaction between the electron-deficient cobalt and oxygen of peroxide adsorbates in Co─OOH- encourages an axially coordinated cobalt oxo complex (O═CoN4 ) to form, the O═CoN4 facilitating the HPOR efficiently at high overpotentials. Low-voltage oxygen evolution reaction guaranteeing low-voltage hydrogen production is successfully demonstrated in the presence of the metal-oxo complex having electron-deficient CoN4 . Hydrogen production by 391 mA cm-2 at 1 V and 870 mA cm-2 at 1.5 V is obtained. Also, the techno-economic benefit of hydrogen peroxide as a hydrogen carrier is evaluated by comparing hydrogen peroxide with other hydrogen carriers such as ammonia and liquid organic hydrogen carriers.

CO2 Reduction to Methane and Ethylene on a Single-Atom Catalyst: A Grand Canonical Quantum Mechanics Study

In recent years, two-dimensional metal-organic frameworks (2D MOF) have attracted great interest for their ease of synthesis and for their catalytic activities and semiconducting properties. The appeal of these materials is that they are layered and easily exfoliated to obtain a monolayer (or few layer) material with interesting optoelectronic properties. Moreover, they have great potential for CO2 reduction to obtain solar fuels with more than one carbon atom, such as ethylene and ethanol, in addition to methane and methanol. In this paper, we explore how a particular class of 2D MOF based on a phthalocyanine core provides the reactive center for the production of ethylene and ethanol. We examine the reaction mechanism using the new grand canonical potential kinetics (GCP-K) or grand canonical quantum mechanics (GC-QM) computational methodology, which obtains reaction rates at constant applied potential to compare directly with experimental results (rather than at constant electrons as in standard QM). We explain the reaction mechanism underlying the formation of methane and ethylene. Here, the key reaction step is direct coupling of CO into CHO, without the usual rate-determining CO-CO dimerization step observed on Cu metal surfaces. Indeed, the 2D MOF behaves like a single-atom catalyst.

Phase Engineering and Synchrotron-Based Study on Two-Dimensional Energy Nanomaterials

In recent years, there has been significant interest in the development of two-dimensional (2D) nanomaterials with unique physicochemical properties for various energy applications. These properties are often derived from the phase structures established through a range of physical and chemical design strategies. A concrete analysis of the phase structures and real reaction mechanisms of 2D energy nanomaterials requires advanced characterization methods that offer valuable information as much as possible. Here, we present a comprehensive review on the phase engineering of typical 2D nanomaterials with the focus of synchrotron radiation characterizations. In particular, the intrinsic defects, atomic doping, intercalation, and heterogeneous interfaces on 2D nanomaterials are introduced, together with their applications in energy-related fields. Among them, synchrotron-based multiple spectroscopic techniques are emphasized to reveal their intrinsic phases and structures. More importantly, various in situ methods are employed to provide deep insights into their structural evolutions under working conditions or reaction processes of 2D energy nanomaterials. Finally, conclusions and research perspectives on the future outlook for the further development of 2D energy nanomaterials and synchrotron radiation light sources and integrated techniques are discussed.

Rational Design of Trimetallic Sulfide Electrodes for Alkaline Water Electrolysis with Ampere-Level Current Density

Electrochemical water splitting is considered an environmentally friendly approach to hydrogen generation. However, it is difficult to achieve high current density and stability. Herein, we design an amorphous/crystalline heterostructure electrode based on trimetallic sulfide over nickel mesh substrate (NiFeMoS/NM), which only needs low overpotentials of 352 mV, 249 mV, and 360 mV to achieve an anodic oxygen evolution reaction (OER) current density of 1 A cm-2 in 1 M KOH, strong alkaline electrolyte (7.6 M KOH), and alkaline-simulated seawater, respectively. More importantly, it also shows superior stability with negligible decay after continuous work for 120 h at 1 A cm-2 in the strong alkaline electrolyte. The excellent OER performance of the as-obtained electrode can be attributed to the strong electronic interactions between different metal atoms, abundant amorphous/crystalline hetero-interfaces, and 3D porous nickel mesh structure. Finally, we coupled NiFeMoS/NM as both the anode and cathode in the anion exchange membrane electrolyzer, which can achieve low cell voltage and high stability at ampere-level current density, demonstrating the great potential of practicability.

Atomically Dispersed Silver Atoms Embedded in NiCo Layer Double Hydroxide Boost Oxygen Evolution Reaction

Bimetallic layered double hydroxides (LDHs) are promising catalysts for anodic oxygen evolution reaction (OER) in alkaline media. Despite good stability, NiCo LDH displays an unsatisfactory OER activity relative to the most robust NiFe LDH and CoFe LDH. Herein, a novel NiCo LDH electrocatalyst modified with single-atom silver grown on carbon cloth (AgSA -NiCo LDH/CC) that exhibits exceptional OER activity and stability in 1.0 m KOH is reported. The AgSA -NiCo LDH/CC catalyst only requires a low overpotential of 192 mV to reach a current density of 10 mA cm-2 , obviously boosting the OER activity of NiCo LDH/CC (410 mV@10 mA cm-2 ). Inspiringly, AgSA -NiCo LDH/CC can maintain its high activity for up to 500 h at a large current density of 100 mA cm-2 , exceeding most single-atom OER catalysts. In situ Raman spectroscopy studies uncover that the in situ formed NiCoOOH during OER is the real active species. Hard X-ray absorption spectrum (XAS) and density functional theory (DFT) calculations validate that single-atom Ag occupying Ni site increases the chemical valence of Ni elements, and then weakens the adsorption of oxygen-contained intermediates on Ni sites, fundamentally accounting for the enhanced OER performance.

Synergy of dual-atom catalysts deviated from the scaling relationship for oxygen evolution reaction

Dual-atom catalysts, particularly those with heteronuclear active sites, have the potential to outperform the well-established single-atom catalysts for oxygen evolution reaction, but the underlying mechanistic understanding is still lacking. Herein, a large-scale density functional theory is employed to explore the feasibility of *O-*O coupling mechanism, which can circumvent the scaling relationship with improving the catalytic performance of N-doped graphene supported Fe-, Co-, Ni-, and Cu-containing heteronuclear dual-atom catalysts, namely, M'M@NC. Based on the constructed activity maps, a rationally designed descriptor can be obtained to predict homonuclear catalysts. Seven heteronuclear and four homonuclear dual-atom catalysts possess high activities that outperform the minimum theoretical overpotential. The chemical and structural origin in favor of *O-*O coupling mechanism thus leading to enhanced reaction activity have been revealed. This work not only provides additional insights into the fundamental understanding of reaction mechanisms, but also offers a guideline for the accelerated discovery of efficient catalysts.

Potential-dependent transition of reaction mechanisms for oxygen evolution on layered double hydroxides

Oxygen evolution reaction (OER) is of crucial importance to sustainable energy and environmental engineering, and layered double hydroxides (LDHs) are among the most active catalysts for OER in alkaline conditions, but the reaction mechanism for OER on LDHs remains controversial. Distinctive types of reaction mechanisms have been proposed for the O-O coupling in OER, yet they compose a coupled reaction network with competing kinetics dependent on applied potentials. Herein, we combine grand-canonical methods and micro-kinetic modeling to unravel that the nature of dominant mechanism for OER on LDHs transitions among distinctive types as a function of applied potential, and this arises from the interplay among applied potential and competing kinetics in the coupled reaction network. The theory-predicted overpotentials, Tafel slopes, and findings are in agreement with the observations of experiments including isotope labelling. Thus, we establish a computational methodology to identify and elucidate the potential-dependent mechanisms for electrochemical reactions.

Reconstructed Ir‒O‒Mo species with strong Brønsted acidity for acidic water oxidation

Surface reconstruction generates real active species in electrochemical conditions; rational regulating reconstruction in a targeted manner is the key for constructing highly active catalyst. Herein, we use the high-valence Mo modulated orthorhombic Pr₃Ir_1-xMo_xO₇ as model to activate lattice oxygen and cations, achieving directional and accelerated surface reconstruction to produce self-terminated Ir‒O_bri‒Mo (O_bri represents the bridge oxygen) active species that is highly active for acidic water oxidation. The doped Mo not only contributes to accelerated surface reconstruction due to optimized Ir‒O covalency and more prone dissolution of Pr, but also affords the improved durability resulted from Mo-buffered charge compensation, thereby preventing fierce Ir dissolution and excessive lattice oxygen loss. As such, Ir‒O_bri‒Mo species could be directionally generated, in which the strong Brønsted acidity of O_bri induced by remaining Mo assists with the facilitated deprotonation of oxo intermediates, following bridging-oxygen-assisted deprotonation pathway. Consequently, the optimal catalyst exhibits the best activity with an overpotential of 259 mV to reach 10 mA cm_geo^-2, 50 mV lower than undoped counterpart, and shows improved stability for over 200 h. This work provides a strategy of directional surface reconstruction to constructing strong Brønsted acid sites in IrO_x species, demonstrating the perspective of targeted electrocatalyst fabrication under in situ realistic reaction conditions.

Molecular Engineering of Metal-Organic Frameworks as Efficient Electrochemical Catalysts for Water Oxidation

Metal-organic framework (MOF) solids with their variable functionalities are relevant for energy conversion technologies. However, the development of electroactive and stable MOFs for electrocatalysis still faces challenges. Here, a molecularly engineered MOF system featuring a 2D coordination network based on mercaptan-metal links (e.g., nickel, as for Ni(DMBD)-MOF) is designed. The crystal structure is solved from microcrystals by a continuous-rotation electron diffraction (cRED) technique. Computational results indicate a metallic electronic structure of Ni(DMBD)-MOF due to the Ni-S coordination, highlighting the effective design of the thiol ligand for enhancing electroconductivity. Additionally, both experimental and theoretical studies indicate that (DMBD)-MOF offers advantages in the electrocatalytic oxygen evolution reaction (OER) over non-thiol (e.g., 1,4-benzene dicarboxylic acid) analog (BDC)-MOF, because it poses fewer energy barriers during the rate-limiting *O intermediate formation step. Iron-substituted NiFe(DMBD)-MOF achieves a current density of 100 mA cm^-2 at a small overpotential of 280 mV, indicating a new MOF platform for efficient OER catalysis.

In Situ Synthesis of NiFeLDH/A-CBp from Pyrolytic Carbon as High-Performance Oxygen Evolution Reaction Catalyst for Water Splitting and Zinc Hydrometallurgy

Nickel-iron-layered double hydroxide (NiFeLDH) is one of the promising catalysts for the oxygen evolution reaction (OER) in alkaline electrolytes, but its conductivity limits its large-scale application. The focus of current work is to explore low-cost, conductive substrates for large-scale production and combine them with NiFeLDH to improve its conductivity. In this work, purified and activated pyrolytic carbon black (CBp) is combined with NiFeLDH to form an NiFeLDH/A-CBp catalyst for OER. CBp not only improves the conductivity of the catalyst but also greatly reduces the size of NiFeLDH nanosheets to increase the activated surface area. In addition, ascorbic acid (AA) is introduced to enhance the coupling between NiFeLDH and A-CBp, which can be evidenced by the increase of Fe-O-Ni peak intensity in FTIR measurement. Thus, a lower overvoltage of 227 mV and larger active surface area of 43.26 mF·cm^-2 are achieved in 1 M KOH solution for NiFeLDH/A-CBp. In addition, NiFeLDH/A-CBp shows good catalytic performance and stability as the anode catalyst for water splitting and Zn electrowinning in alkaline electrolytes. In Zn electrowinning with NiFeLDH/A-CBp, the low cell voltage of 2.08 V at 1000 A·m^-2 results in lower energy consumption of 1.78 kW h/Kg_Zn, which is nearly half of the 3.40 kW h/Kg_Zn of industrial electrowinning. This work demonstrates the new application of high-value-added CBp in hydrogen production from electrolytic water and zinc hydrometallurgy to realize the recycling of waste carbon resources and reduce the consumption of fossil resources.

Dynamic orbital hybridization triggered spin-disorder renormalization via super-exchange interaction for oxygen evolution reaction

The oxygen evolution reaction (OER) underpins many aspects of energy storage and conversion in modern industry and technology, but which still be suffering from the dilemma of sluggish reaction kinetics and poor electrochemical performance. Different from the viewpoint of nanostructuring, this work focuses on an intriguing dynamic orbital hybridization approach to renormalize the disordering spin configuration in porous noble-metal-free metal-organic frameworks (MOFs) to accelerate the spin-dependent reaction kinetics in OER. Herein, we propose an extraordinary super-exchange interaction to reconfigure the domain direction of spin nets at porous MOFs through temporarily bonding with dynamic magnetic ions in electrolytes under alternating electromagnetic field stimulation, in which the spin renormalization from disordering low-spin state to high-spin state facilitates rapid water dissociation and optimal carrier migration, leading to a spin-dependent reaction pathway. Therefore, the spin-renormalized MOFs demonstrate a mass activity of 2,095.1 A gmetal-1 at an overpotential of 0.33 V, which is about 5.9 time of pristine ones. Our findings provide a insight into reconfiguring spin-related catalysts with ordering domain directions to accelerate the oxygen reaction kinetics.

Atomically Strained Metal Sites for Highly Efficient and Selective Photooxidation

Strain engineering is an attractive strategy for improving the intrinsic catalytic performance of heterogeneous catalysts. Manipulating strain on the short-range atomic scale to the local structure of the catalytic sites is still challenging. Herein, we successfully achieved atomic strain modulation on ultrathin layered vanadium oxide nanoribbons by an ingenious intercalation chemistry method. When trace sodium cations were introduced between the V₂O₅ layers (Na⁺-V₂O₅), the V-O bonds were stretched by the atomically strained vanadium sites, redistributing the local charges. The Na⁺-V₂O₅ demonstrated excellent photooxidation performance, which was approximately 12 and 14 times higher than that of pristine V₂O₅ and VO₂, respectively. Complementary spectroscopy analysis and theoretical calculations confirmed that the atomically strained Na⁺-V₂O₅ had a high surficial charge density, improving the activation of oxygen molecules and contributing to the excellent photocatalytic property. This work provides a new approach for the rational design of strain-equipped catalysts for selective photooxidation reactions.

In situ Observation of Porosity Formation in Porous Single-crystalline TiO2 Monolith for Enhanced and Stable Catalytic CO Oxidation

Introducing pores in single crystals creates a new type of porous materials that incorporate porosity and structural coherence. Herein, we use in situ transmission electron microscopy to disclose the porosity formation by converting KTiOPO₄ (KTP) single crystals into porous single-crystalline (PSC) TiO₂ monoliths in a solid-solid transformation. The isolated crystalline nuclei of TiO₂ clusters with identical lattice orientation on KTP surface moves TiO₂ /KTP interface toward mother phase for growing PSC TiO₂ monoliths. The relative density in PSC TiO₂ monoliths dominates porosity while the macroscopic dimensions remain unchanged in the transformation. The single-crystalline nature of porous architecture stabilizes oxygen vacancy to activate lattice oxygen while the three-dimensional percolation enhances species diffusion. PSC TiO₂ monoliths with deposited Pt clusters show enhanced and stable catalytic CO oxidation in air at ∼75 °C for 200 hours of operation.

Identification of Active Sites Formed on Cobalt Oxyhydroxide in Glucose Electrooxidation

Transition-metal-based oxyhydroxides are efficient catalysts in biomass electrooxidation towards fossil-fuel-free production of valuable chemicals. However, identification of active sites remains elusive. Herein, using cobalt oxyhydroxide (CoOOH) as the archetype and the electrocatalyzed glucose oxidation reaction (GOR) as the model reaction, we track dynamic transformation of the electronic and atomic structure of the catalyst using a suite of operando and ex situ techniques. We reveal that two types of reducible Co³⁺ -oxo species are afforded for the GOR, including adsorbed hydroxyl on Co³⁺ ion (μ₁ -OH-Co³⁺ ) and di-Co³⁺ -bridged lattice oxygen (μ₂ -O-Co³⁺ ). Moreover, theoretical calculations unveil that μ₁ -OH-Co³⁺ is responsible for oxygenation, while μ₂ -O-Co³⁺ mainly contributes to dehydrogenation, both as key oxidative steps in glucose-to-formate transformation. This work provides a framework for mechanistic understanding of the complex near-surface chemistry of metal oxyhydroxides in biomass electrorefining.

Unraveling Sequential Oxidation Kinetics and Determining Roles of Multi-Cobalt Active Sites on Co3O4 Catalyst for Water Oxidation

The multi-redox mechanism involving multi-sites has great implications to dictate the catalytic water oxidation. Understanding the sequential dynamics of multi-steps in oxygen evolution reaction (OER) cycles on working catalysts is a highly important but challenging issue. Here, using quasi-operando transient absorption (TA) spectroscopy and a typical photosensitization strategy, we succeeded in resolving the sequential oxidation kinetics involving multi-active sites for water oxidation in OER catalytic cycle, with Co₃O₄ nanoparticles as model catalysts. When OER initiates from fast oxidation of surface Co²⁺ ions, both surface Co²⁺ and Co³⁺ ions are active sites of the multi-cobalt centers for water oxidation. In the sequential kinetics (Co²⁺ → Co³⁺ → Co⁴⁺), the key characteristic is fast oxidation and slow consumption for all the cobalt species. Due to this characteristic, the Co⁴⁺ intermediate distribution plays a determining role in OER activity and results in the slow overall OER kinetics. These insights shed light on the kinetic understanding of water oxidation on heterogeneous catalysts with multi-sites.

Nanowire photochemical diodes for artificial photosynthesis

Artificial photosynthesis can provide a solution to our current energy needs by converting small molecules such as water or carbon dioxide into useful fuels. This can be accomplished using photochemical diodes, which interface two complementary light absorbers with suitable electrocatalysts. Nanowire semiconductors provide unique advantages in terms of light absorption and catalytic activity, yet great control is required to integrate them for overall fuel production. In this review, we journey across the progress in nanowire photoelectrochemistry (PEC) over the past two decades, revealing design principles to build these nanowire photochemical diodes. To this end, we discuss the latest progress in terms of nanowire photoelectrodes, focusing on the interplay between performance, photovoltage, electronic band structure, and catalysis. Emphasis is placed on the overall system integration and semiconductor-catalyst interface, which applies to inorganic, organic, or biologic catalysts. Last, we highlight further directions that may improve the scope of nanowire PEC systems.

Activated Ni-O-Ir Enhanced Electron Transfer for Boosting Oxygen Evolution Reaction Activity of LaNi1-x Irx O3

Tuning the structure of the active center of catalysts to atomic level provides the most efficient utilization of the active component, which plays an especially important role for precious metals. In this study, the liquid phase ion exchange method is used to introduce atomic Ir into LaNiO₃ perovskite oxide, which shows excellent catalytic performance in the oxygen evolution reaction (OER). The catalyst, LaNi_0.96 Ir_0.04 O₃ , with the optimal concentration of Ir, displays an overpotential of just 280 mV at 10 mA cm^-2 . The introduced Ir enriches the surface electron density significantly, which not only improves site-to-site electron transfer between O and Ni sites but also allows stable adsorption of the intermediates. The results of cyclic voltammetry tests reveal the superior overpotential and remarkable efficiency of the OER process because of the strong interactions in Ni-O-Ir. Moreover, the Ir atom inhibits the participation of a lattice oxygen oxidation mechanism (LOM) in LaNiO₃ that guarantees the stability of the catalyst in alkaline conditions. It is anticipated that this work will be instrumental for the preparation and study of a broad range of atomic metal-doped perovskite oxides for water splitting.

Determining the hydronium pK[Formula: see text] at platinum surfaces and the effect on pH-dependent hydrogen evolution reaction kinetics

Electrocatalytic hydrogen evolution reaction (HER) is critical for green hydrogen generation and exhibits distinct pH-dependent kinetics that have been elusive to understand. A molecular-level understanding of the electrochemical interfaces is essential for developing more efficient electrochemical processes. Here we exploit an exclusively surface-specific electrical transport spectroscopy (ETS) approach to probe the Pt-surface water protonation status and experimentally determine the surface hydronium pKa [Formula: see text] 4.3. Quantum mechanics (QM) and reactive dynamics using a reactive force field (ReaxFF) molecular dynamics (RMD) calculations confirm the enrichment of hydroniums (H3O[Formula: see text]) near Pt surface and predict a surface hydronium pKa of 2.5 to 4.4, corroborating the experimental results. Importantly, the observed Pt-surface hydronium pKa correlates well with the pH-dependent HER kinetics, with the protonated surface state at lower pH favoring fast Tafel kinetics with a Tafel slope of 30 mV per decade and the deprotonated surface state at higher pH following Volmer-step limited kinetics with a much higher Tafel slope of 120 mV per decade, offering a robust and precise interpretation of the pH-dependent HER kinetics. These insights may help design improved electrocatalysts for renewable energy conversion.

Ce-induced regulation of electron density enhanced the catalytic activity of Co-Mn oxides for water oxidation

The incorporation of Ce into Co-Mn oxides induced the charge redistribution of Co and Mn via electronic coupling, which facilitated the Co³⁺/Co⁴⁺ transition. Thus, the overpotential at 10 mA cm^-2 was reduced significantly by 73 mV for the oxygen evolution reaction after Ce doping.

OH spectator at IrMo intermetallic narrowing activity gap between alkaline and acidic hydrogen evolution reaction

The sluggish kinetics of the hydrogen evolution reaction in base has resulted in large activity gap between acidic and alkaline electrolytes. Here, we present an intermetallic IrMo electrocatalyst supported on carbon nanotubes that exhibits a specific activity of 0.95 mA cm-2 at the overpotential of 15 mV, which is 14.4 and 9.5 times of those for Ir/C and Pt/C, respectively. More importantly, its activities in base are fairly close to that in acidic electrolyte and the activity gap between acidic and alkaline media is only one fourth of that for Ir/C. DFT calculations reveal that the stably-adsorbed OH spectator at Mo site of IrMo can stabilize the water dissociation product, resulting in a thermodynamically favorable water dissociation process. Beyond offering an advanced electrocatalyst, this work provides a guidance to rationally design the desirable HER electrocatalysts for alkaline water splitting by the stably-adsorbed OH spectator.