The Pivotal Role of s-, p-, and f-Block Metals in Water Electrolysis: Status Quo and Perspectives

Operando Spectroscopic Monitoring of Metal Chalcogenides for Overall Water Splitting: New Views of Active Species and Sites

Metal-based chalcogenides exhibit great promise for overall water splitting, yet their intrinsic catalytic reaction mechanisms remain to be fully understood. In this work, we employed operando X-ray absorption (XAS) and in situ Raman spectroscopy to elucidate the structure-activity relationships of low-crystalline cobalt sulfide (L-CoS) catalysts toward overall water splitting. The operando results for L-CoS catalyzing the alkaline hydrogen evolution reaction (HER) demonstrate that the cobalt centers in the bulk are predominantly coordinated by sulfur atoms, which undergo a kinetic structural rearrangement to generate metallic cobalt in S-Co-Co-S moieties as the true catalytically active species. In comparison, during the acidic HER, L-CoS undergoes local structural optimization of Co centers, and H2 production proceeds with adsorption/desorption of key intermediates atop the Co-S-Co configurations. Further operando characterizations highlight the crucial formation of high-valent Co4+ species in L-CoS for the alkaline oxygen evolution reaction (OER), and the formation of such active species was found to be far more facile than in crystalline Co3O4 and Co-LDH references. These insights offer a clear picture of the complexity of active species and site formation in different media, and demonstrate how their restructuring influences the catalytic activity.

Interfacial Engineering of MoS2@CoS2 Heterostructure Electrocatalysts for Effective pH-Universal Hydrogen Evolution Reaction

The practical utilization of the hydrogen evolution reaction (HER) necessitates the creation of electrocatalysts that are both efficient and abundant in earth elements, capable of operating effectively within a wide pH range. However, this objective continues to present itself as an arduous obstacle. In this research, we propose the incorporation of sulfur vacancies in a novel heterojunction formed by MoS2@CoS2, designed to exhibit remarkable catalytic performances. This efficacy is attributed to the advantageous combination of the low work function and space charge zone at the interface between MoS2 and CoS2 in the heterojunction. The MoS2@CoS2 heterojunction manifests outstanding hydrogen evolution activity over an extensive pH range. Remarkably, achieving a current density of 10 mA cm-2 in aqueous solutions 1.0 M KOH, 0.5 M H2SO4, and 1.0 M phosphate-buffered saline (PBS), respectively, requires only an overpotential of 48, 62, and 164 mV. The Tafel slopes for each case are 43, 32, and 62 mV dec-1, respectively. In this study, the synergistic effect of MoS2 and CoS2 is conducive to electron transfer, making the MoS2@CoS2 heterojunction show excellent electrocatalytic performance. The synergistic effects arising from the heterojunction and sulfur vacancy not only contribute to the observed catalytic prowess but also provide a valuable model and reference for the exploration of other efficient electrocatalysts. This research marks a significant stride toward overcoming the challenges associated with developing electrocatalysts for practical hydrogen evolution applications.

Integrated In Situ Fabrication of CuO Nanorod-Decorated Polymer Membranes for the Catalytic Flow-Through Reduction of p-Nitrophenol

We developed a novel method to fabricate copper nanorods in situ in a poly(ether sulfone) (15 wt %) casting solution by a sonochemical reduction of Cu2+ ions with NaBH4. The main twist is the addition of ethanol to remove excess NaBH4 through Cu(0) catalyzed ethanolysis. This enabled the direct use of the resulting copper-containing casting dispersions for membrane preparation by liquid nonsolvent-induced phase separation and led to full utilization of the copper source, generating zero metal waste. We characterized the copper nanorods as presented in the membranes via scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and UV/vis spectroscopy. We could demonstrate that the rapid immobilization from reducing conditions led to the membrane incorporation of copper nanorods in a state of high reactivity, which also promoted the complete oxidation to CuO after fabrication. We further observed a large aspect ratio and crystal straining of the nanorods, likely resulting from growth around the matrix polymer. The entanglement with poly(ether sulfone) further facilitated a selective presentation at the pore surface of the final CuO-decorated membranes. The membranes also exhibit high water permeances of up to 2800 L/m2hbar. Our catalytic membranes achieved exceptionally high activities in the aqueous flow-through reduction of p-nitrophenol (p-NP), with turnover frequencies of up to 115 h-1, even surpassing those of other state-of-the-art catalytic membranes that incorporate Pd or Ag. Additionally, we demonstrated that catalytic hydrolysis of the reducing agent in water can lead to hydrogen gas formation and blocking of active sites during continuous catalytic p-NP hydrogenation. We illustrated that the accompanying conversion loss can be mitigated by facilitated gas transport in the water-filled pores, which is dependent on the orientation of the pore size gradient and the flow direction.

Understanding Advanced Transition Metal-Based Two Electron Oxygen Reduction Electrocatalysts from the Perspective of Phase Engineering

Non-noble transition metal (TM)-based compounds have recently become a focal point of extensive research interest as electrocatalysts for the two electron oxygen reduction (2e- ORR) process. To efficiently drive this reaction, these TM-based electrocatalysts must bear unique physiochemical properties, which are strongly dependent on their phase structures. Consequently, adopting engineering strategies toward the phase structure has emerged as a cutting-edge scientific pursuit, crucial for achieving high activity, selectivity, and stability in the electrocatalytic process. This comprehensive review addresses the intricate field of phase engineering applied to non-noble TM-based compounds for 2e- ORR. First, the connotation of phase engineering and fundamental concepts related to oxygen reduction kinetics and thermodynamics are succinctly elucidated. Subsequently, the focus shifts to a detailed discussion of various phase engineering approaches, including elemental doping, defect creation, heterostructure construction, coordination tuning, crystalline design, and polymorphic transformation to boost or revive the 2e- ORR performance (selectivity, activity, and stability) of TM-based catalysts, accompanied by an insightful exploration of the phase-performance correlation. Finally, the review proposes fresh perspectives on the current challenges and opportunities in this burgeoning field, together with several critical research directions for the future development of non-noble TM-based electrocatalysts.

Interfacial π-p Electron Coupling Prompts Hydrogen Evolution Reaction Activity in Acidic Electrolyte

The thermodynamically stable 2H-phase MoS2 is a brilliant material toward hydrogen evolution reaction (HER) owing to its excellent Gibbs free energy of hydrogen adsorption. Nevertheless, the poor intrinsic properties of 2H-MoS2 limit its electrocatalytic performances toward HER. In this work, graphitic carbon nitride covalently bridging 2H-MoS2 (MoS2/GCN) is proposed to construct robust HER electrocatalysts. The strong π-p electron coupling between the delocalized π electrons of GCN and the localized p electrons of S atoms sufficiently expose active sites and accelerate the reaction kinetics. To be specific, MoS2/GCN exhibits remarkable HER activity (160 mV at 10 mA·cm-2) and long-term durability. Importantly, MoS2/GCN also provides great potential for industrial application. Density functional theory (DFT) calculations disclose that the π-p electron coupling at the MoS2/GCN interface regulates the electronic structure of S atoms, consequently providing enhanced HER performance. This work presents a feasible pathway to develop advanced electrocatalysts for energy conversions.

Alkaline Water Electrolysis for Green Hydrogen Production

ConspectusThe global energy landscape is undergoing significant change. Hydrogen is seen as the energy carrier of the future and will be a key element in the development of more sustainable industry and society. However, hydrogen is currently produced mainly from fossil fuels, and this needs to change. Alkaline water electrolysis with advanced technology has the most significant potential for this transition to produce large-scale green hydrogen by utilizing renewable energy. The assembly of industrial electrolyzer plants is more complex on a larger scale, but it follows a basic working principle, which involves two half-cells of anode and cathode sites where the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) occur. Out of the two reactions, the OER is more challenging both thermodynamically and kinetically. Besides having access to renewable electricity, developing durable and abundant electrocatalysts for the OER remains a challenge in large-scale alkaline water electrolysis. Among different physicochemical properties, the electrocatalyst surface and its interaction with water and reaction intermediates, as well as formed molecular hydrogen and oxygen, play an essential role in the catalytic performance and the reaction mechanism. In particular, the binding strengths between the catalyst surface and intermediates determine the rate-limiting step and electrocatalytic performance.This Account gives some insights into the status of the hydrogen economy and basic principles of alkaline water electrolysis by covering its fundamentals as well as industrial developments. Further, the HER and OER reaction mechanisms of alkaline water electrolysis and selected electrocatalyst progress for both half-reactions are briefly discussed. The Adsorbate Evolution Mechanism and the Lattice Oxygen Mechanism for the OER are explained with specific references. This Account also deliberates on the author's selected contributions to the development of transition metal-based electrocatalysts for alkaline water electrolysis with an emphasis on OER. The focus is particularly given to the enhancement of intrinsic activity, the role of eg-filling, phase segregation, and defect structure of cobalt-based electrocatalysts for OER. Structural modification and phase transformation of the cobalt oxide electrocatalyst under working conditions are further deliberated. In addition, the creation of new active surface species and the activation of cobalt- and nickel-based electrocatalysts through iron uptake from the alkaline electrolyte are discussed. In the end, this Account provides a brief overview of challenges related to large-scale production and utilization of green hydrogen.

In Situ Insertion of Silicon Nanowires into Hollow Porous Co/NC Polyhedra Enabling Large-Current-Density Hydrogen Evolution Electrocatalysis

N-doped carbon (NC)-encapsulated transition metal (TM) nanocomposites are considered as alternatives to Pt-based hydrogen evolution reaction (HER) electrocatalysts; however, their poor electron transfer and mass diffusion capability at high current densities hinder their practical application. Herein, an oriented coupling strategy for the in situ grafting of ultrafine Co nanoparticle-embedded hollow porous C polyhedra onto Si nanowires (Co/NC-HP@Si-NWs) is proposed to address this concern. Experimental investigations reveal that the intimate coupling between the Si-NW and Co/NC nanocage forms a multithreaded conductive network, lowering the energy barrier for internal electron transfer. When functionalized as an HER electrocatalyst in 0.5 m H2 SO4 , Co/NC-HP@Si-NWs deliver overpotentials as low as 57 and 440 mV at 10 and 500 mA cm-2 , respectively, which are much better than those of the pristine Co/NC-HP. Moreover, Co/NC-HP@Si-NWs show an outstanding cycle durability of 24 h at 10 and 500 mA cm-2 . The findings of this study are expected to inspire revolutionary work on the development of Si-mediated TM-based electrocatalysts for the HER.

Ru nanoclusters anchored on boron- and nitrogen-doped carbon for a highly efficient hydrogen evolution reaction in alkaline seawater

Electrochemical seawater splitting is an intriguing strategy for green hydrogen production. Constructing advanced electrocatalysts for the hydrogen evolution reaction (HER) in seawater is extremely demanded for accelerating the sluggish kinetic process. Herein, a Ru nanocluster anchored on boron- and nitrogen-doped carbon (Ru/NBC) catalyst was successfully synthesized for the HER in alkaline/seawater electrolytes. Remarkably, Ru/NBC exhibits outstanding activity and durability, delivering low overpotentials@10 mA cm-2 in 1.0 M KOH (30 mV) and 1.0 M KOH + seawater electrolyte (35 mV), outperforming Pt/C, Ru/NC, Ru/BC and Ru/C. Additionally, Ru/NBC also provides a high specific activity of 0.093 mA cm-2ECSA at an overpotential of 150 mV, which is higher than those of Ru/NC, Ru/BC and Ru/C, respectively. Density functional theory calculation results demonstrate that the Ru-B formed interfacial chemical bond can regulate the electronic structure of Ru active sites of Ru/NBC, which can facilitate the adsorption of water and hydrogen in alkaline media. This work provides a feasible strategy to fabricate outstanding electrocatalysts for the HER in alkaline/alkaline seawater electrolytes.

Conversion of Natural Biowaste into Energy Storage Materials and Estimation of Discharge Capacity through Transfer Learning in Li-Ion Batteries

To simultaneously reduce the cost of environmental treatment of discarded food waste and the cost of energy storage materials, research on biowaste conversion into energy materials is ongoing. This work employs a solid-state thermally assisted synthesis method, transforming natural eggshell membranes (NEM) into nitrogen-doped carbon. The resulting NEM-coated LFP (NEM@LFP) exhibits enhanced electrical and ionic conductivity that can promote the mobility of electrons and Li-ions on the surface of LFP. To identify the optimal synthesis temperature, the synthesis temperature is set to 600, 700, and 800 °C. The NEM@LFP synthesized at 700 °C (NEM 700@LFP) contains the most pyrrolic nitrogen and has the highest ionic and electrical conductivity. When compared to bare LFP, the specific discharge capacity of the material is increased by approximately 16.6% at a current rate of 0.1 C for 50 cycles. In addition, we introduce innovative data-driven experiments to observe trends and estimate the discharge capacity under various temperatures and cycles. These data-driven results corroborate and support our experimental analysis, highlighting the accuracy of our approach. Our work not only contributes to reducing environmental waste but also advances the development of efficient and eco-friendly energy storage materials.

A Facile Molecular Approach to Amorphous Nickel Pnictides and Their Reconstruction to Crystalline Potassium-Intercalated γ-NiOOHx Enabling High-Performance Electrocatalytic Water Oxidation and Selective Oxidation of 5-Hydroxymethylfurfural

The low-temperature molecular precursor approach can be beneficial to conventional solid-state methods, which require high temperatures and lead to relatively large crystalline particles. Herein, a novel, single-step, room-temperature preparation of amorphous nickel pnictide (NiE; EP, As) nanomaterials is reported, starting from NaOCE(dioxane)n and NiBr2 (thf)1.5 . During application for the oxygen evolution reaction (OER), the pnictide anions leach, and both materials fully reconstruct into nickel(III/IV) oxide phases (similar to γ-NiOOH) comprising edge-sharing (NiO6 ) layers with intercalated potassium ions and a d-spacing of 7.27 Å. Remarkably, the intercalated γ-NiOOHx phases are nanocrystalline, unlike the amorphous nickel pnictide precatalysts. This unconventional reconstruction is fast and complete, which is ascribed to the amorphous nature of the nanostructured NiE precatalysts. The obtained γ-NiOOHx can effectively catalyse the OER for 100 h at a high current density (400 mA cm-2 ) and achieves outstandingly high current densities (>600 mA cm-2 ) for the selective, value-added oxidation of 5-hydroxymethylfurfural (HMF). The NiP-derived γ-NiOOHx shows a higher activity for both processes due to more available active sites. It is anticipated that the herein developed, effective, room-temperature molecular synthesis of amorphous nickel pnictide nanomaterials can be applied to other functional transition-metal pnictides.

Immobilization of Oxyanions on the Reconstructed Heterostructure Evolved from a Bimetallic Oxysulfide for the Promotion of Oxygen Evolution Reaction

Efficient and durable oxygen evolution reaction (OER) requires the electrocatalyst to bear abundant active sites, optimized electronic structure as well as robust component and mechanical stability. Herein, a bimetallic lanthanum-nickel oxysulfide with rich oxygen vacancies based on the La2O2S prototype is fabricated as a binder-free precatalyst for alkaline OER. The combination of advanced in situ and ex situ characterizations with theoretical calculation uncovers the synergistic effect among La, Ni, O, and S species during OER, which assures the adsorption and stabilization of the oxyanion [Formula: see text] onto the surface of the deeply reconstructed porous heterostructure composed of confining NiOOH nanodomains by La(OH)3 barrier. Such coupling, confinement, porosity and immobilization enable notable improvement in active site accessibility, phase stability, mass diffusion capability and the intrinsic Gibbs free energy of oxygen-containing intermediates. The optimized electrocatalyst delivers exceptional alkaline OER activity and durability, outperforming most of the Ni-based benchmark OER electrocatalysts.

Challenges for Hybrid Water Electrolysis to Replace the Oxygen Evolution Reaction on an Industrial Scale

To enable a future society based on sun and wind energy, transforming electricity into chemical energy in the form of fuels is crucial. This transformation can be achieved in an electrolyzer performing water splitting, where at the anode, water is oxidized to oxygen-oxygen evolution reaction (OER)-to produce protons and electrons that can be combined at the cathode to form hydrogen-hydrogen evolution reaction (HER). While hydrogen is a desired fuel, the obtained oxygen has no economic value. A techno-economically more suitable alternative is hybrid water electrolysis, where value-added oxidation reactions of abundant organic feedstocks replace the OER. However, tremendous challenges remain for the industrial-scale application of hybrid water electrolysis. Herein, these challenges, including the higher kinetic overpotentials of organic oxidation reactions compared to the OER, the small feedstock availably and product demand of these processes compared to the HER (and carbon dioxide reduction), additional purifications costs, and electrocatalytic challenges to meet the industrially required activities, selectivities, and especially long-term stabilities are critically discussed. It is anticipated that this perspective helps the academic research community to identify industrially relevant research questions concerning hybrid water electrolysis.

Homogeneous regulation of arranged polymorphic manganese dioxide nanocrystals as cathode materials for high-performance zinc-ion batteries

Rechargeable aqueous zinc-ion batteries have emerged as attractive energy storage devices by virtue of their low cost, high safety and eco-friendliness. However, zinc-ion cathodes are bottlenecked by their vulnerable crystal structures in the process of zinc embedding and significant capacity fading during long-term cycling. Herein, we report the rational and homogeneous regulation of polycrystalline manganese dioxide (MnO₂) nanocrystals as zinc cathodes via a surfactant template-assisted strategy. Benefiting from the homogeneous regulation, MnO₂ nanocrystals with an ordered crystal arrangement, including nanorod-like polyvinylpyrrolidone-manganese dioxide (PVP-MnO₂), nanowire-like sodium dodecyl benzene sulfonate-manganese dioxide and nanodot-like cetyltrimethylammonium bromide-manganese dioxide, are obtained. Among these, the nanorod-like PVP-MnO₂ nanocrystals exhibit stable long-life cycling of 210 mAh g^-1 over 180 cycles at a high rate of 0.3 A g^-1 and with a high capacity retention of 84% over 850 cycles at a high rate of 1 A g^-1. The good performance of this cathode significantly results from the facile charge and mass transfer at the interface between the electrode and electrolyte, featuring the crystal stability and uniform morphology of the arranged MnO₂ nanocrystals. This work provides crucial insights into the development of advanced MnO₂ cathodes for low-cost and high-performance rechargeable aqueous zinc-ion batteries.

Evolution of Carbonate-Intercalated γ-NiOOH from a Molecularly Derived Nickel Sulfide (Pre)Catalyst for Efficient Water and Selective Organic Oxidation

The development of a competent (pre)catalyst for the oxygen evolution reaction (OER) to produce green hydrogen is critical for a carbon-neutral economy. In this aspect, the low-temperature, single-source precursor (SSP) method allows the formation of highly efficient OER electrocatalysts, with better control over their structural and electronic properties. Herein, a transition metal (TM) based chalcogenide material, nickel sulfide (NiS), is prepared from a novel molecular complex [Ni^II (PyHS)₄ ][OTf]₂ (1) and utilized as a (pre)catalyst for OER. The NiS (pre)catalyst requires an overpotential of only 255 mV to reach the benchmark current density of 10 mA cm^-2 and shows 63 h of chronopotentiometry (CP) stability along with over 95% Faradaic efficiency in 1 m KOH. Several ex situ measurements and quasi in situ Raman spectroscopy uncover that NiS irreversibly transformed to a carbonate-intercalated γ-NiOOH phase under the alkaline OER conditions, which serves as the actual active structure for the OER. Additionally, this in situ formed active phase successfully catalyzes the selective oxidation of alcohol, aldehyde, and amine-based organic substrates to value-added chemicals, with high efficiencies.

Oxygen Evolution/Reduction Reaction Catalysts: From In Situ Monitoring and Reaction Mechanisms to Rational Design

The oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are core steps of various energy conversion and storage systems. However, their sluggish reaction kinetics, i.e., the demanding multielectron transfer processes, still render OER/ORR catalysts less efficient for practical applications. Moreover, the complexity of the catalyst-electrolyte interface makes a comprehensive understanding of the intrinsic OER/ORR mechanisms challenging. Fortunately, recent advances of in situ/operando characterization techniques have facilitated the kinetic monitoring of catalysts under reaction conditions. Here we provide selected highlights of recent in situ/operando mechanistic studies of OER/ORR catalysts with the main emphasis placed on heterogeneous systems (primarily discussing first-row transition metals which operate under basic conditions), followed by a brief outlook on molecular catalysts. Key sections in this review are focused on determination of the true active species, identification of the active sites, and monitoring of the reactive intermediates. For in-depth insights into the above factors, a short overview of the metrics for accurate characterizations of OER/ORR catalysts is provided. A combination of the obtained time-resolved reaction information and reliable activity data will then guide the rational design of new catalysts. Strategies such as optimizing the restructuring process as well as overcoming the adsorption-energy scaling relations will be discussed. Finally, pending current challenges and prospects toward the understanding and development of efficient heterogeneous catalysts and selected homogeneous catalysts are presented.

Mild construction of an Fe-B-O based flexible electrode toward highly efficient alkaline simulated seawater splitting

It is essential to construct self-supporting electrodes based on earth-abundant iron borides in a mild and economical manner for grid-scale hydrogen production. Herein, a series of highly efficient, flexible, robust, and scalable Fe-B-O@FeB_x modified on hydrophilic cloth (denoted as Fe-B-O@FeB_x/HC, 10 cm × 10 cm) are fabricated by mild electroless plating. The overpotentials and Tafel slope values for the hydrogen and oxygen evolution reactions are 59 mV and 57.62 mV dec^-1 and 181 mV and 65.44 mV dec^-1, respectively; only 1.462 V is required to achieve 10 mA cm^-2 during overall water splitting (OWS). Fe-B-O@FeB_x/HC maintains its high catalytic activity for more than 7 days at an industrial current density (400 mA cm^-2), owing to the loosened popcorn-like Fe-B-O@FeB_x that is firmly loaded on a 2D-layered and mechanically robust substrate along with its fast charge and mass transfer kinetics. The chimney effect of core-shell borides@(oxyhydro)oxides enhances the OWS performance and protects the inner metal borides from further corrosion. Moreover, the flexible Fe-B-O@FeB_x/HC electrode has a low cost for grid-scale hydrogen production ($2.97 kg^-1). The proposed strategy lays a solid foundation for universal preparation, large-scale hydrogen production and practical applications thereof.

Reviving Oxygen Evolution Electrocatalysis of Bulk La-Ni Intermetallics via Gaseous Hydrogen Engineering

A hydrogen processing strategy is developed to enable bulk LaNi₅ to attain high activity and long-term stability toward the electrocatalytic oxygen evolution reaction (OER). By a combination of in situ Raman and quasi in situ X-ray absorption (XAS) spectra, secondary-electron-excited scanning transmission electron microscopy (STEM) patterns as well as the Rietveld method and density functional theory (DFT) calculations, it is discovered that hydrogen-induced lattice distortion, grain refinement, and particle cracks dictate the effective reconstruction of the LaNi₅ surface into a porous hetero-nanoarchitecture composed of uniformly confined active γ-NiOOH nanocrystals by La(OH)₃ layer in the alkaline OER process. This significantly optimizes the charge transfer, structural integrity, active-site exposure, and adsorption energy toward the reaction intermediates. Benefiting from these merits, the overpotential (322 mV) at 100 mA cm^-2 for the hydrogen-processed OER catalyst deposited on nickel foam is reduced by 104 mV as compared to the original phase. Notably, it exhibits remarkable stability for 10 days at an industrial-grade current density of more than 560 mA cm^-2 in alkaline media.

Fabrication of Ultra-Durable and Flexible NiPx -Based Electrode toward High-Efficient Alkaline Seawater Splitting at Industrial Grade Current Density

Designing nonprecious metal-based electrocatalysts to yield sustainable hydrogen energy by large-scale seawater electrolysis is challenging to global emissions of carbon neutrality and carbon peaking. Herein, a series of highly efficient, economical, and robust Ni-P-based nanoballs grown on the flexible and anti-corrosive hydrophobic asbestos (NiP_x @HA) is synthesized by electroless plating at 25 °C toward alkaline simulated seawater splitting. On the basis of the strong chemical attachment between 2D layered substrate and nickel-rich components, robust hexagonal Ni₅ P₄ crystalline modification, and fast electron transfer capability, the overpotentials during hydrogen/oxygen evolution reaction (HER/OER) are 208 and 392 mV at 200 mA cm^-2 , and the chronopotentiometric measurement at 500 mA cm^-2 lasts for over 40 days. Additionally, the versatile strategy is broadly profitable for industrial applications and enables multi-elemental doping (iron/cobalt/molybdenum/boron/tungsten), flexible substrate employment (nickel foam/filter paper/hydrophilic cloth), and scalable synthesis (22 cm × 22 cm). Density functional theory (DFT) also reveals that the optimized performance is due to the fundamental effect of incorporating O-source into Ni₅ P₄ . Therefore, this work exhibits a complementary strategy in the construction of NiP_x -based electrodes and offers bright opportunities to produce scalable hydrogen effectively and stably in alkaline corrosive electrolytes.

Ce-Modified Flowerlike NiFe-MOF Nanostructure Based on Ion Competitive Coordination for Enhancing the Oxygen Evolution Reaction

Metal-organic framework (MOF) has become a popular electrocatalyst for the oxygen evolution reaction (OER) because of its large specific surface area and adjustable porosity. Nevertheless, the electrochemical performance of MOFs has been greatly limited by poor intrinsic conductivity and catalytic activity. Herein, we report a Ce-doped nanoflower-like MOF material Ce@NiFe-MOF-5 via a facile ion competitive coordination effect and doping method. Benefiting from the nanoflower structure formed by the stacking of nanosheets, a large number of active sites can be exposed, which favors electron/mass transfer during water oxidation. The coordination substitution of Ce ions not only promoted an increase in the number of active sites on the surface of the nanosheets but also optimized the electronic structure of pristine NiFe-MOF. The well-designed Ce@NiFe-MOF-5 catalysts exhibited superior OER performance under basic conditions, which only required an overpotential of 258 mV at a current density of 10 mA cm^-2 and a Tafel slope of 54.44 mV dec^-1. Moreover, when Ce@NiFe-MOF-5 served as an anode and Pt/C as a cathode, the two-electrode system only needed 1.56 V to drive overall water splitting at 10 mA cm^-2.

Sustainable and practical formation of carbon-carbon and carbon-heteroatom bonds employing organo-alkali metal reagents

Metal-catalysed cross-coupling reactions are amongst the most widely used methods to directly construct new bonds. In this connection, sustainable and practical protocols, especially transition metal-catalysed cross-coupling reactions, have become the focus in many aspects of synthetic chemistry due to their high efficiency and atom economy. This review summarises recent advances from 2012 to 2022 in the formation of carbon-carbon bonds and carbon-heteroatom bonds by employing organo-alkali metal reagents.

Effect of Proton Transfer on Electrocatalytic Water Oxidation by Manganese Phosphates

The effect of proton transfer on water oxidation has hardly been measurably established in heterogeneous electrocatalysts. Herein, two isomorphous manganese phosphates (NH₄ MnPO₄  ⋅ H₂ O and KMnPO₄  ⋅ H₂ O) were designed to form an ideal platform to study the effect of proton transfer on water oxidation. The hydrogen-bonding network in NH₄ MnPO₄  ⋅ H₂ O has been proven to be solely responsible for its better activity. The differences of the proton transfer kinetics in the two materials indicate a fast proton hopping transfer process with a low activation energy in NH₄ MnPO₄  ⋅ H₂ O. In addition, the hydrogen-bonding network can effectively promote the proton transfer between adjacent Mn sites and further stabilize the Mn^III -OH intermediates. The faster proton transfer results in a higher proportion of zeroth-order in [H⁺ ] for OER. Thus, proton transfer-affected electrocatalytic water oxidation has been measurably observed to bring detailed insights into the mechanism of water oxidation.

In Situ Coupling of Carbon Dots with Co-ZIF Nanoarrays Enabling Highly Efficient Oxygen Evolution Electrocatalysis

Metal-organic frameworks (MOFs) are regarded as one promising class of precatalysts for electrocatalytic oxygen evolution reaction (OER), yet most of them suffer from poor conductivity and lack of coordinatively unsaturated metal sites, which hinders the fast electrochemical reconstruction and thus a poor OER activity. To address this issue, a unique heterocomposite has been constructed by in situ inserting carbon dots (CDs) into cobalt-based zeolitic imidazolate framework (Co-ZIF) nanosheet arrays (Co-ZIF/CDs/CC) in the presence of carbon cloth (CC) via one-pot coprecipitation for alkaline OER. Benefiting from the synergism between CDs and Co-ZIF subunits such as superior conductivity, strong charge interaction as well as abundant metal sites exposure, the Co-ZIF/CDs/CC exhibits an enhanced promotion effect for OER and contributes to the deep phase transformation from CDs-coupled Co-ZIF to CDs-coupled active CoOOH. As expected, the achieved Co-ZIF/CDs/CC only requires an overpotential of 226 mV to deliver 10 mA cm^-2 in 1.0 M KOH, which is lower than that of Co-ZIF/CC and superior to most previously reported CC-supported MOF precatalysts. Moreover, it can also maintain a large current density of 100 mA cm^-2 for 24 h with negligible activity decay.

Waste-Derived Catalysts for Water Electrolysis: Circular Economy-Driven Sustainable Green Hydrogen Energy

The sustainable production of green hydrogen via water electrolysis necessitates cost-effective electrocatalysts. By following the circular economy principle, the utilization of waste-derived catalysts significantly promotes the sustainable development of green hydrogen energy. Currently, diverse waste-derived catalysts have exhibited excellent catalytic performance toward hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and overall water electrolysis (OWE). Herein, we systematically examine recent achievements in waste-derived electrocatalysts for water electrolysis. The general principles of water electrolysis and design principles of efficient electrocatalysts are discussed, followed by the illustration of current strategies for transforming wastes into electrocatalysts. Then, applications of waste-derived catalysts (i.e., carbon-based catalysts, transitional metal-based catalysts, and carbon-based heterostructure catalysts) in HER, OER, and OWE are reviewed successively. An emphasis is put on correlating the catalysts' structure-performance relationship. Also, challenges and research directions in this booming field are finally highlighted. This review would provide useful insights into the design, synthesis, and applications of waste-derived electrocatalysts, and thus accelerate the development of the circular economy-driven green hydrogen energy scheme.

Effect of Surface‐Adsorbed and Intercalated (Oxy)anions on the Oxygen Evolution Reaction

As the kinetically demanding oxygen evolution reaction (OER) is crucial for the decarbonization of our society, a wide range of (pre)catalysts with various non‐active‐site elements (e.g., Mo, S, Se, N, P, C, Si…) have been investigated. Thermodynamics dictate that these elements oxidize during industrial operation. The formed oxyanions are water soluble and thus predominantly leach in a reconstruction process. Nevertheless, recently, it was unveiled that these thermodynamically stable (oxy)anions can adsorb on the surface or intercalate in the interlayer space of the active catalyst. There, they tune the electronic properties of the active sites and can interact with the reaction intermediates, changing the OER kinetics and potentially breaking the persisting OER *OH/*OOH scaling relations. Thus, the addition of (oxy)anions to the electrolyte opens a new design dimension for OER catalysis and the herein discussed observations deepen the understanding of the role of anions in the OER.

Self-supported molybdenum nickel oxide catalytic electrode designed via molecular cluster-mediated electroplating and electrochemical activation for an efficient and durable oxygen evolution reaction

Efficient and durable nonprecious catalysts for the oxygen evolution reaction (OER) are crucial for practical water electrolysis for hydrogen production. A self-supported OER catalytic electrode with sufficient exposure of the catalyst and tight anchoring onto the current collector is vital for the catalytic activity and stability, and is therefore deemed to be a preferable tactic to enhance water electrolysis performance. Herein, a polyoxometalate (POM) molecular cluster-mediated electroplating and activation tactics are proposed to design a self-supported molybdenum nickel oxide (MoNiO_x) catalytic electrode for the OER. The MoNiO_x active layer can anchor tightly onto the Ni foam current collector with sufficient surface exposure and high structural stability, therefore enabling high alkali OER catalytic efficiency (222 mV at 10 mA cm^-2) and robust durability (only slight decay in catalytic efficiency upon 12 days of chronopotentiometry (V-t) test). Moreover, the easily processable electroplating and active protocol can serve as a general approach to prepare other OER catalytic electrodes by altering the reactants and current collectors. The current work paves a facile and universal way to design a highly active and durable molybdenum (Mo) based hybrid catalytic electrode for OER via molecular cluster-assisted electroplating and activation treatment.

Composition Engineering of Amorphous Nickel Boride Nanoarchitectures Enabling Highly Efficient Electrosynthesis of Hydrogen Peroxide

Developing advanced electrocatalysts with exceptional two electron (2e^- ) selectivity, activity, and stability is crucial for driving the oxygen reduction reaction (ORR) to produce hydrogen peroxide (H₂ O₂ ). Herein, a composition engineering strategy is proposed to flexibly regulate the intrinsic activity of amorphous nickel boride nanoarchitectures for efficient 2e^- ORR by oriented reduction of Ni²⁺ with different amounts of BH₄ ^- . Among borides, the amorphous NiB₂ delivers the 2e^- selectivity close to 99% at 0.4 V and over 93% in a wide potential range, together with a negligible activity decay under prolonged time. Notably, an ultrahigh H₂ O₂ production rate of 4.753 mol g_cat ^-1 h^-1 is achieved upon assembling NiB₂ in the practical gas diffusion electrode. The combination of X-ray absorption and in situ Raman spectroscopy, as well as transient photovoltage measurements with density functional theory, unequivocally reveal that the atomic ratio between Ni and B induces the local electronic structure diversity, allowing optimization of the adsorption energy of Ni toward *OOH and reducing of the interfacial charge-transfer kinetics to preserve the OO bond.