A corrosion-resistant RuMoNi catalyst for efficient and long-lasting seawater oxidation and anion exchange membrane electrolyzer

Boosting urea-assisted water splitting over P-MoO2@CoNiP through Mo leaching/reabsorption coupling CoNiP reconstruction

Combining the urea oxidation reaction (UOR) with the hydrogen evolution reaction (HER) is an effective technology for energy-saving hydrogen production. Herein, a bifunctional electrocatalyst with CoNiP nanosheet coating on P-doped MoO2 nanorods (P-MoO2@CoNiP) is obtained via a two-step hydrothermal followed a phosphorization process. The catalyst demonstrates exceptional alkaline HER performance due to the formation of MoO2 and the dissolution/absorption of Mo. Meanwhile, the inclusion of Co and P in the P-MoO2@CoNiP catalyst facilitated the formation of NiOOH, enhancing UOR performance. Density functional theory calculations reveal that the hydrogen adsorption Gibbs free energy (ΔGH*) of P-MoO2@CoNiP is closer to 0 eV than CoNiP, favoring the HER. The catalyst only needs -0.08 and 1.38 V to reach 100 mA cm-2 for catalyzing the HER and UOR, respectively. The full urea electrolysis system driven by P-MoO2@CoNiP requires 1.51 V to achieve 100 mA cm-2, 120 mV lower than the traditional water electrolysis.

Hetero-structured Ru-Mo2C nanoparticles loaded on N,P co-doped carbon for a pH universal hydrogen evolution reaction

Considering the extensive research studies on Ru and Mo2C for the hydrogen evolution reaction (HER), the construction of heterostructure catalysts containing both Ru and Mo2C nanoparticles can further improve the catalytic activity by the synergistic effect of different species. In this work, we report the synthesis of N,P co-doped carbon coated Ru and Mo2C nanoparticles for the HER using a ZnMo metal-organic framework (MOF) as the precursor. The addition of phosphomolybdic acid during the synthesis of a Zn-MOF not only provides a Mo source for the formation of Mo2C, but also induces a nano-bowl structure. After anchoring RuCl3 in the ZnMo-MOF and thermal annealing, Ru and Mo2C nanoparticles encapsulated in N,P doped carbon (Ru-Mo2C@NPC) were synthesized and the nano-bowl morphology was well preserved. Due to the co-existence of the highly active catalytic species Ru and Mo2C, a large specific surface area owing to the evaporation of Zn during the calcination process, and the nano-bowl-like morphology that boosts mass transfer, Ru-Mo2C@NPC exhibits good catalytic activity for the HER over a wide pH range, with overpotentials of 62, 64 and 170 mV in 0.5 M H2SO4, 1 M KOH and 1 M PBS solution at 10 mA cm-2, surpassing the values for many Ru and Mo2C based catalysts. This work provides a feasible route for designing high performance HER catalysts.

Recent advances in developing nanoscale electro-/photocatalysts for hydrogen production: modification strategies, charge-carrier characterizations, and applications

For clean hydrogen (H2) production, electrocatalysis and photocatalysis are widely regarded as promising technologies to counter the increasing energy crisis. However, developing applicable catalysts with high H2 production performances still poses a challenge. In this review, state-of-the-art nanoscale electrocatalysts for water electrolysis and photocatalysts for water splitting, tailored for different reaction environments, including acidic electrolytes, alkaline electrolytes, pure water, seawater, and hydrohalic acids, are systematically presented. In particular, modification approaches such as doping, morphology control, heterojunction/homojunction construction, as well as the integration of cocatalysts and single atoms for efficient charge transfer and separation are examined. Furthermore, the unique properties of these upgraded catalysts and the mechanisms of promoted H2 production are also analyzed by elucidating the charge carrier dynamics revealed by photophysical and photoelectrochemical characterization methods. Finally, perspectives and outlooks on future developments for H2 production using advanced electrocatalysts and photocatalysts are proposed.

Coordination Engineering of Carbon Dots and Mn in Co-Based Phosphides for Highly Efficient Seawater Splitting at Ampere-Level Current Density

Direct electrolysis of seawater to generate hydrogen is an attractive approach for storing renewable energy. However, direct seawater splitting suffers from low current density and limited operating stability, which severely hinders its industrialization. Herein, a promising strategy is reported to obtain a nano needle-like array catalyst-CDs-Mn-CoxP on nickel foam, in which the Mn─O─C bond tightly binds Mn, Carbon dots (CDs), and CoxP together. The coordination engineering of CDs and Mn not only effectively regulates the electronic structure of CoxP, but also endows the as-prepared catalyst with selectivity and marked long-term stability at ampere-level current density. Low overpotentials of 208 and 447 mV are required to achieve 1000 mA cm-2 for hydrogen evolution reaction (HER) and Oxygen evolution reaction (OER) in simulated seawater, respectively. Cell potentials of 1.78 and 1.86 V are needed to reach 500 and 1000 mA cm-2 in alkaline seawater along with excellent durability for 350 h. DFT studies have verified that the introduction of Mn and CDs effectively shifts the d-band center of Co-3d toward higher energy, thereby strengthening the adsorption of intermediates and enhancing the catalytic activity. This study sheds light on the development of highly effective and stable catalysts for large-scale seawater electrolysis.

Stability of electrocatalytic OER: from principle to application

Hydrogen energy, derived from the electrolysis of water using renewable energy sources such as solar, wind, and hydroelectric power, is considered a promising form of energy to address the energy crisis. However, the anodic oxygen evolution reaction (OER) poses limitations due to sluggish kinetics. Apart from high catalytic activity, the long-term stability of electrocatalytic OER has garnered significant attention. To date, several research studies have been conducted to explore stable electrocatalysts for the OER. A comprehensive review is urgently warranted to provide a concise overview of the recent advancements in the electrocatalytic OER stability, encompassing both electrocatalyst and device developments. This review aims to succinctly summarize the primary factors influencing OER stability, including morphological/phase change and electrocatalyst dissolution, as well as mechanical detachment, alongside chemical, mechanical, and operational degradation observed in devices. Furthermore, an overview of contemporary approaches to enhance stability is provided, encompassing electrocatalyst design (structural regulation, protective layer coating, and stable substrate anchoring) and device optimization (bipolar plates, gas diffusion layers, and membranes). Hopefully, more attention will be paid to ensuring the stable operation of electrocatalytic OER and the future large-scale water electrolysis applications. This review presents design principles aimed at addressing challenges related to the stability of electrocatalytic OER.

Stable Seawater Electrolysis Over 10 000 H via Chemical Fixation of Sulfate on NiFeBa-LDH

Although hydrogen production through seawater electrolysis combined with offshore renewable energy can significantly reduce the cost, the corrosive anions in seawater strictly limit the commercialization of direct seawater electrolysis technology. Here, it is discovered that electrolytic anode can be uniformly protected in a seawater environment by constructing NiFeBa-LDH catalyst assisted with additional SO4 2- in the electrolyte. In experiments, the NiFeBa-LDH achieves unprecedented stability over 10 000 h at 400 mA cm-2 in both alkaline saline electrolyte and alkaline seawater. Characterizations and simulations reveal that the atomically dispersed Ba2+ enables the chemical fixation of free SO4 2- on the surface, which generates a dense SO4 2- layer to repel Cl- along with the preferentially adsorbed SO4 2- in the presence of an applied electric field. In terms of the simplicity and effectiveness of catalyst design, it is confident that it can be a beacon for the commercialization of seawater electrolysis technology.

Aerophobic/Hydrophilic Nickel-Iron Sulfide Nanoarrays for Energy-Saving Hydrogen Production from Seawater Splitting Assisted by Sulfion Oxidation Reaction

Electrolysis of infinite seawater is a promising and sustainable approach for clean hydrogen production. However, it remains a big challenge to accomplish corrosion-resistant and chlorine-free seawater electrolysis at low power input. Herein, the bimetallic nickel-iron sulfide-based electrocatalytic nanoarrays are constructed by a facile hydrothermal sulfidation of redox-etched iron foam (IF), which manifests an effective and reliable strategy for the sulfion oxidation reaction (SOR) to assist alkaline seawater electrolysis for the achievement of energy-saving hydrogen production and value-added sulfion upcycling. The resulting NiFeSx/FeNi3/IF required 0.353 and 0.415 V vs RHE for SOR at current densities of 50 and 100 mA cm-2, which are considerably lower than the theoretical potential of the oxygen evolution reaction (OER, 1.23 V vs RHE). In situ spectroscopy analysis demonstrated efficient sulfion oxidation on the surface of NiFeSx/FeNi3/IF. Furthermore, the NiFeSx/FeNi3/IF-assembled electrolyzer delivered a greatly reduced cell voltage of 0.92 V at 50 mA cm-2 and maintains excellent durability for 30 h, achieving high Faradaic efficiency for both hydrogen production and sulfion degradation. In addition, under natural sunlight (660.4 W m-2), only a 0.947 V voltage of the solar panel smoothly powers the SOR-coupled seawater electrolysis for green hydrogen production and economic sulfur recovery.

Progress in Anode Stability Improvement for Seawater Electrolysis to Produce Hydrogen

Seawater electrolysis for hydrogen production is a sustainable and economical approach that can mitigate the energy crisis and global warming issues. Although various catalysts/electrodes with excellent activities have been developed for high-efficiency seawater electrolysis, their unsatisfactory durability, especially for anodes, severely impedes their industrial applications. In this review, attention is paid to the factors that affect the stability of anodes and the corresponding strategies for designing catalytic materials to prolong the anode's lifetime. In addition, two important aspects-electrolyte optimization and electrolyzer design-with respect to anode stability improvement are summarized. Furthermore, several methods for rapid stability assessment are proposed for the fast screening of both highly active and stable catalysts/electrodes. Finally, perspectives on future investigations aimed at improving the stability of seawater electrolysis systems are outlined.

Confined Growth of Highly Ordered Metal Atomic Arrays for Seawater Oxidation

Metal atom catalysts have been among the most important research objects due to their specific physical and chemical properties. However, precise control of the anchoring of metal atoms is still challenging to achieve. Cobalt and iridium atomic arrays formed sequentially ordered stable arrays in graphdiyne (GDY) triangular cavities depending on their intrinsic chemical properties and interactions. The success of this method was attributed to multifunctional integration of GDY, enabling selective growth from one to several atoms and various atomic densities. The bimetallic atom arrays show several advantages resulting from reducibility of acetylene bonds, space limiting effect, incomplete charge transfer between GDY and metal atoms, and sp-C hybridized triple bond skeleton. This well-designed system exhibits unprecedented oxygen evolution reaction (OER) performance with a mass activity of 2.6 A mgcat. -1 at a low overpotential of 300 mV, which is 216.6 times higher than the state-of-the-art IrO2 catalyst, and long-term stability.

Boosting oxygen evolution reaction by FeNi hydroxide-organic framework electrocatalyst toward alkaline water electrolyzer

The oxygen evolution reaction plays a vital role in modern energy conversion and storage, and developing cost-efficient oxygen evolution reaction catalysts with industrially relevant activity and durability is highly desired but still challenging. Here, we report an efficient and durable FeNi hydroxide organic framework nanosheet array catalyst that competently affords long-term oxygen evolution reaction at industrial-grade current densities in alkaline electrolyte. The desirable high-intensity performance is attributed to three aspects as follows. First, two-dimensional nanosheet porous arrays with maximum specific surface facilitate mass/charge transfer to accommodate high-current-density catalysis. Second, in situ derived FeNi hydroxide motifs offer bimetallic synergistic catalysis centers with high intrinsic activity. Third, carboxyl ligands alleviate metal oxidation favorable for charge tolerability against peroxidation dissolution under strong polarization. As a result, this catalyst requires an overpotential of only 280 mV to deliver high current density up to 1 A/cm2 with long durability over 1000 h. Moreover, an alkaline water electrolyzer with this catalyst alternative demonstrates an increased economic effectiveness compared to commercial levels at present.

Recycling Spent Ternary Cathodes to Oxygen Evolution Catalysts for Pure Water Anion-Exchange Membrane Electrolysis

Recycling spent lithium-ion batteries (LIBs) to efficient water-splitting electrocatalysts is a promising and sustainable technology route for green hydrogen production by renewables. In this work, a fluorinated ternary metal oxide (F-TMO) derived from spent LIBs was successfully converted to a robust water oxidation catalyst for pure water electrolysis by utilizing an anion-exchange membrane. The optimized catalyst delivered a high current density of 3.0 A cm-2 at only 2.56 V and a durability of >300 h at 0.5 A cm-2, surpassing the noble-metal IrO2 catalyst. Such excellent performance benefits from an artificially endowed interface layer on the F-TMO, which renders the exposure of active metal (oxy)hydroxide sites with a stabilized configuration during pure water operation. Compared to other metal oxides (i.e., NiO, Co3O4, MnO2), F-TMO possesses a higher stability number of 2.4 × 106, indicating its strong potential for industrial applications. This work provides a feasible way of recycling waste LIBs to valuable electrocatalysts.

Highly Sustainable h-BN Encapsulated MoS2 Hydrogen Evolution Catalysts

Despite the importance of the stability of the 2D catalysts in harsh electrolyte solutions, most studies have focused on improving the catalytic performance of molybdenum disulfide (MoS2) catalysts rather than the sustainability of hydrogen evolution. In previous studies, the vulnerability of MoS2 crystals is reported that the moisture and oxygen molecules can cause the oxidation of MoS2 crystals, accelerating the degradation of crystal structure. Therefore, optimization of catalytic stability is crucial for approaching practical applications in 2D catalysts. Here, it is proposed that monolayered MoS2 catalysts passivated with an atomically thin hexagonal boron nitride (h-BN) layer can effectively sustain hydrogen evolution reaction (HER) and demonstrate the ultra-high current density (500 mA cm⁻2 over 11 h) and super stable (64 h at 150 mA cm⁻2) catalytic performance. It is further confirmed with density functional theory (DFT) calculations that the atomically thin h-BN layer effectively prevents direct adsorption of water/acid molecules while allowing the protons to be adsorbed/penetrated. The selective penetration of protons and prevention of crystal structure degradation lead to maintained catalytic activity and maximized catalytic stability in the h-BN covered MoS2 catalysts. These findings propose a promising opportunity for approaching the practical application of 2D MoS2 catalysts having long-term stability at high-current operation.

Engineering d-p Orbital Hybridization in Mo-O Species of Medium-Entropy Metal Oxides as Highly Active and Stable Electrocatalysts toward Ampere-Level Water/Seawater Splitting

Optimizing the electronic structure of electrocatalysts is of particular importance to enhance the intrinsic activity of active sites in water/seawater. Herein, a series of medium-entropy metal oxides of X(NiMo)O2/NF (X = Mn, Fe, Co, Cu and Zn) is designed via a rapid carbothermal shocking method. Among them, the optimized medium-entropy metal oxide (FeNiMo)O2/NF delivered remarkable HER performance, where the overpotentials as low as 110 and 141 mV are realized at 1000 mA cm-2 (@60 °C) in water and seawater. Meanwhile, medium-entropy metal oxide (FeNiMo)O2/NF only required overpotentials of as low as 330 and 380 mV to drive 1000 mA cm-2 for OER in water and seawater (@60 °C). Theoretical calculations showed that the multiple-metal synergistic effect in medium-entropy metal oxides can effectively enhance the d-p orbital hybridization of Mo─O bond, reduce the energy barrier of H* adsorbed at the Mo sites. Meanwhile, Fe sites in medium-entropy metal oxide can act as the real OER active center, resulting in a good bifunctional activity. In all, this work provides a feasible strategy for the development of highly active and stable medium-entropy metal oxide electrocatalysts for ampere-level water/seawater splitting.

Stabilizing NiFe sites by high-dispersity of nanosized and anionic Cr species toward durable seawater oxidation

Electrocatalytic H2 production from seawater, recognized as a promising technology utilizing offshore renewables, faces challenges from chloride-induced reactions and corrosion. Here, We introduce a catalytic surface where OH- dominates over Cl- in adsorption and activation, which is crucial for O2 production. Our NiFe-based anode, enhanced by nearby Cr sites, achieves low overpotentials and selective alkaline seawater oxidation. It outperforms the RuO2 counterpart in terms of lifespan in scaled-up stacks, maintaining stability for over 2500 h in three-electrode tests. Ex situ/in situ analyses reveal that Cr(III) sites enrich OH-, while Cl- is repelled by Cr(VI) sites, both of which are well-dispersed and close to NiFe, enhancing charge transfer and overall electrode performance. Such multiple effects fundamentally boost the activity, selectively, and chemical stability of the NiFe-based electrode. This development marks a significant advance in creating durable, noble-metal-free electrodes for alkaline seawater electrolysis, highlighting the importance of well-distributed catalytic sites.

Arming Amorphous NiMoO4 on Nickel Phosphide Enables Highly Stable Alkaline Seawater Oxidation

Seawater electrolysis holds tremendous promise for the generation of green hydrogen (H2). However, the system of seawater-to-H2 faces significant hurdles, primarily due to the corrosive effects of chlorine compounds, which can cause severe anodic deterioration. Here, a nickel phosphide nanosheet array with amorphous NiMoO4 layer on Ni foam (Ni2P@NiMoO4/NF) is reported as a highly efficient and stable electrocatalyst for oxygen evolution reaction (OER) in alkaline seawater. Such Ni2P@NiMoO4/NF requires overpotentials of just 343 and 370 mV to achieve industrial-level current densities of 500 and 1000 mA cm-2, respectively, surpassing that of Ni2P/NF (470 and 555 mV). Furthermore, it maintains consistent electrolysis for over 500 h, a significant improvement compared to that of Ni2P/NF (120 h) and Ni(OH)2/NF (65 h). Electrochemical in situ Raman spectroscopy, stability testing, and chloride extraction analysis reveal that is situ formed MoO4 2-/PO4 3- from Ni2P@NiMoO4 during the OER test to the electrode surface, thus effectively repelling Cl- and hindering the formation of harmful ClO-.

Electron Redistribution of Ru Site on MoO2@NiMoO4 Support for Efficient Ampere-Level Current Density Electrolysis of Alkaline Seawater

Seawater electrolysis is a promising but challenging strategy to generate carbon-neutral hydrogen. A grand challenge for hydrogen evolution reaction (HER) from alkaline seawater electrolysis is the development of efficient and stable electrocatalysts to overcome the limitation of sluggish kinetics. Here, a 3D nanorod hybrid catalyst is reported, which comprises heterostructure MoO2@NiMoO4 supported Ru nanoparticles (Ru/ MoO2@NiMoO4) with a size of ≈5 nm. Benefitting from the effect of strongly coupled interaction, Ru/MoO2@NiMoO4 catalyst exhibits a remarkable alkaline seawater hydrogen evolution performance, featured by a low overpotential of 184 mV at a current density of 1.0 A cm-2, superior to commercial Pt/C (338 mV). Experimental observations demonstrate that the heterostructure MoO2@NiMoO4 as an electron-accepting support makes the electron transfer from the Ru nanoparticles to MoO2, and thereby implements the electron redistribution of Ru site. Mechanistic analysis elucidates that the electron redistribution of active Ru site enhances the ability of hydrogen desorption, thereby promoting alkaline seawater HER kinetics and finally leading to a satisfactory catalysis performance at ampere-level current density of alkaline seawater electrolysis.

Ultra-Thin RuIr Alloy as Durable Electrocatalyst for Seawater Hydrogen Evolution Reaction

The development of efficient, high-performance catalysts for hydrogen evolution reaction (HER) remains a significant challenge, especially in seawater media. Here, RuIr alloy catalysts are prepared by the polyol reduction method. Compared with single-metal catalysts, the RuIr alloy catalysts exhibited higher activity and stability in seawater electrolysis due to their greater number of reactive sites and solubility resistance. The RuIr alloy has an overpotential of 75 mV@10 mA cm-2, which is similar to that of Pt/C (73 mV), and can operate stably for 100 hours in alkaline seawater. Density functional theory (DFT) calculations indicate that hydrogen atoms adsorbed at the top sites of Ru and Ir atoms are more favorable for HER and are most likely to be the reactive sites. This work provides a reference for developing highly efficient and stable catalysts for seawater electrolysis.

Energy-saving hydrogen production by seawater electrolysis coupling tip-enhanced electric field promoted electrocatalytic sulfion oxidation

Hydrogen production by seawater electrolysis is significantly hindered by high energy costs and undesirable detrimental chlorine chemistry in seawater. In this work, energy-saving hydrogen production is reported by chlorine-free seawater splitting coupling tip-enhanced electric field promoted electrocatalytic sulfion oxidation reaction. We present a bifunctional needle-like Co3S4 catalyst grown on nickel foam with a unique tip structure that enhances the kinetic rate by improving the current density in the tip region. The assembled hybrid seawater electrolyzer combines thermodynamically favorable sulfion oxidation and cathodic seawater reduction can enable sustainable hydrogen production at a current density of 100 mA cm-2 for up to 504 h. The hybrid seawater electrolyzer has the potential for scale-up industrial implementation of hydrogen production by seawater electrolysis, which is promising to achieve high economic efficiency and environmental remediation.

A N-doped carbon substrate makes the Ru-Co alloy an efficient electrocatalyst for pH-universal seawater splitting

Designing electrocatalysts for seawater splitting remains challenging. A Ru-Co alloy supported by an N-doped carbon substrate catalyst has been designed using etching and a low-temperature treatment method. Studies show that the superior performance of this catalyst is related to the hollow-structured N-doped carbon frame and surface reconstruction of the Ru-Co alloy.

Seawater electrolysis for fuels and chemicals production: fundamentals, achievements, and perspectives

Seawater electrolysis for the production of fuels and chemicals involved in onshore and offshore plants powered by renewable energies offers a promising avenue and unique advantages for energy and environmental sustainability. Nevertheless, seawater electrolysis presents long-term challenges and issues, such as complex composition, potential side reactions, deposition of and poisoning by microorganisms and metal ions, as well as corrosion, thus hindering the rapid development of seawater electrolysis technology. This review focuses on the production of value-added fuels (hydrogen and beyond) and fine chemicals through seawater electrolysis, as a promising step towards sustainable energy development and carbon neutrality. The principle of seawater electrolysis and related challenges are first introduced, and the redox reaction mechanisms of fuels and chemicals are summarized. Strategies for operating anodes and cathodes including the development and application of chloride- and impurity-resistant electrocatalysts/membranes are reviewed. We comprehensively summarize the production of fuels and chemicals (hydrogen, carbon monoxide, sulfur, ammonia, etc.) at the cathode and anode via seawater electrolysis, and propose other potential strategies for co-producing fine chemicals, even sophisticated and electronic chemicals. Seawater electrolysis can drive the oxidation and upgrading of industrial pollutants or natural organics into value-added chemicals or degrade them into harmless substances, which would be meaningful for environmental protection. Finally, the perspective and prospects are outlined to address the challenges and expand the application of seawater electrolysis.

Built-In Electric Field Boosted Overall Water Electrolysis at Large Current Density for the Heterogeneous Ir/CoMoO4 Nanosheet Arrays

Advanced bifunctional electrocatalysts are essential for propelling overall water splitting (OWS) progress. Herein, relying on the obvious difference in the work function of Ir (5.44 eV) and CoMoO4 (4.03 eV) and the constructed built-in electric field (BEF), an Ir/CoMoO4/NF heterogeneous catalyst, with ultrafine Ir nanoclusters (1.8 ± 0.2 nm) embedded in CoMoO4 nanosheet arrays on the surface of nickel foam skeleton, is reported. Impressively, the Ir/CoMoO4/NF shows remarkable electrocatalytic bifunctionality toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), especially at large current densities, requiring only 13 and 166 mV to deliver 10 and 1000 mA cm-2 for HER and 196 and 318 mV for OER. Furthermore, the Ir/CoMoO4/NF||Ir/CoMoO4/NF electrolyzer demands only 1.43 and 1.81 V to drive 10 and 1000 mA cm-2 for OWS. Systematical theoretical calculations and tests show that the formed BEF not only optimizes interfacial charge distribution and the Fermi level of both Ir and CoMoO4, but also reduces the Gibbs free energy (ΔGH*, from 0.25 to 0.03 eV) and activation energy (from 13.6 to 8.9 kJ mol-1) of HER, the energy barrier (from 3.47 to 1.56 eV) and activation energy (from 21.1 to 13.9 kJ mol-1) of OER, thereby contributing to the glorious electrocatalytic bifunctionality.

Enthralling Anodic Protection by Molybdate on High-Entropy Alloy-Based Electrocatalyst for Sustainable Seawater Oxidation

Efficient and sustainable seawater electrolysis is still limited due to the interference of chloride corrosion at the anode. The designing of suitable electrocatalysts is one of the crucial ways to boost electrocatalytic activity. However, the approach may fall short as achieving high current density often occurs in chlorine evolution reaction (CER)-dominating potential regions. Thereby, apart from developing an OER-active high-entropy alloy-based electrocatalyst, the present study also offers a unique way to protect anode surface under high current density or potential by using MoO4 2- as an effective inhibitor during seawater oxidation. The wide variation of d-band center of high-entropy alloy-based electrocatalyst allows great oxygen evolution reaction (OER) proficiency exhibiting an overpotential of 230 mV at current density of 20 mA cm-2. Besides, the electrocatalyst demonstrates impressive stability over 500 h at high current density of 1 A cm-2 or at a high oxidation potential of 2.0 V versus RHE in the presence of a molybdate inhibitor. Theoretical and experimental studies reveal MoO4 2- electrostatically accumulated at anode surface due to higher adsorption ability, thereby creating a protective layer against chlorides without affecting OER.

In-situ direct seawater electrolysis using floating platform in ocean with uncontrollable wave motion

Direct hydrogen production from inexhaustible seawater using abundant offshore wind power offers a promising pathway for achieving a sustainable energy industry and fuel economy. Various direct seawater electrolysis methods have been demonstrated to be effective at the laboratory scale. However, larger-scale in situ demonstrations that are completely free of corrosion and side reactions in fluctuating oceans are lacking. Here, fluctuating conditions of the ocean were considered for the first time, and seawater electrolysis in wave motion environment was achieved. We present the successful scaling of a floating seawater electrolysis system that employed wind power in Xinghua Bay and the integration of a 1.2 Nm3 h-1-scale pilot system. Stable electrolysis operation was achieved for over 240 h with an electrolytic energy consumption of 5 kWh Nm-3 H2 and a high purity (>99.9%) of hydrogen under fluctuating ocean conditions (0~0.9 m wave height, 0~15 m s-1 wind speed), which is comparable to that during onshore water electrolysis. The concentration of impurity ions in the electrolyte was low and stable over a long period of time under complex and changing scenarios. We identified the technological challenges and performances of the key system components and examined the future outlook for this emerging technology.

Self-supported Ru-doped NiMoO4 for efficient hydrogen evolution with 1000 mA cm-2 at a low overpotential

Self-supported Ru-doped NiMoO4 (Ru-NiMoO4) is synthesized on commercial NiMo foam. The Ru-NiMoO4 exhibits extremely high performance for electrocatalytic hydrogen evolution with a small overpotential of 170.6 mV to afford a current density of 1000 mA cm-2, and excellent durability for 150 hours in alkaline solution.

Self-protecting CoFeAl-layered double hydroxides enable stable and efficient brine oxidation at 2 A cm-2

Low-energy consumption seawater electrolysis at high current density is an effective way for hydrogen production, however the continuous feeding of seawater may result in the accumulation of Cl-, leading to severe anode poisoning and corrosion, thereby compromising the activity and stability. Herein, CoFeAl layered double hydroxide anodes with excellent oxygen evolution reaction activity are synthesized and delivered stable catalytic performance for 350 hours at 2 A cm-2 in the presence of 6-fold concentrated seawater. Comprehensive analysis reveals that the Al3+ ions in electrode are etched off by OH- during oxygen evolution reaction process, resulting in M3+ vacancies that boost oxygen evolution reaction activity. Additionally, the self-originated Al(OH)n- is found to adsorb on the anode surface to improve stability. An electrode assembly based on a micropore membrane and CoFeAl layered double hydroxide electrodes operates continuously for 500 hours at 1 A cm-2, demonstrating their feasibility in brine electrolysis.

Nickel-Cobalt Bimetal Hierarchical Hollow Nanosheets for Efficient Oxygen Evolution in Seawater

The electrochemical splitting of seawater is promising but also challenging for sustainable hydrogen gas production. Herein, ZIF-67 nanosheets are grown on nickel foam and then etched by Ni2+ in situ to obtain a hierarchical hollow nanosheets structure, which demonstrates outstanding OER performance in alkaline seawater (355 mV at 100 mA cm-2). Diven by a silicon solar panel, an overall electrolysis energy efficiency of 62% is achieved at a high current of 100 mA cm-2 in seawater electrolytes. This work provides a new design route for improving the catalytic activity of metal organic framework materials.

Transpassive Metal Dissolution vs. Oxygen Evolution Reaction: Implication for Alloy Stability and Electrocatalysis

Multi-principal element alloys (MPEAs) are gaining interest in corrosion and electrocatalysis research due to their electrochemical stability across a broad pH range and the design flexibility they offer. Using the equimolar CrCoNi alloy, we observe significant metal dissolution in a corrosive electrolyte (0.1 M NaCl, pH 2) concurrently with the oxygen evolution reaction (OER) in the transpassive region, despite the absence of hysteresis in polarization curves or other obvious corrosion indicators. We present a characterization scheme to delineate the contribution of OER and alloy dissolution, using scanning electrochemical microscopy (SECM) for OER-onset detection, and quantitative chemical analysis with inductively coupled-mass spectrometry (ICP-MS) and ultraviolet visible light (UV/Vis) spectrometry to elucidate metal dissolution processes. In situ electrochemical atomic force microscopy (EC-AFM) revealed that the transpassive metal dissolution on CrCoNi is dominated by intergranular corrosion. These results have significant implications for the stability of MPEAs in corrosion systems, emphasizing the necessity of analytically determining metal ions released from MPEA electrodes into the electrolyte when evaluating Faradaic efficiencies of OER catalysts. The release of transition metal ions not only reduces the Faradaic efficiency of electrolyzers but may also cause poisoning and degradation of membranes in electrochemical reactors.

Reconstructing Hydrogen-Bond Network for Efficient Acidic Oxygen Evolution

Developing highly active oxygen evolution reaction (OER) catalysts in acidic conditions is a pressing demand for proton-exchange membrane water electrolysis. Manipulating proton character at the electrified interface, as the crux of all proton-coupled electrochemical reactions, is highly desirable but elusive. Herein we present a promising protocol, which reconstructs a connected hydrogen-bond network between the catalyst-electrolyte interface by coupling hydrophilic units to boost acidic OER activity. Modelling on N-doped-carbon-layer clothed Mn-doped-Co3O4 (Mn-Co3O4@CN), we unravel that the hydrogen-bond interaction between CN units and H2O molecule not only drags the free water to enrich the surface of Mn-Co3O4 but also serves as a channel to promote the dehydrogenation process. Meanwhile, the modulated local charge of the Co sites from CN units/Mn dopant lowers the OER barrier. Therefore, Mn-Co3O4@CN surpasses RuO2 at high current density (100 mA cm-2 @ ~538 mV).

Efficient bubble/precipitate traffic enables stable seawater reduction electrocatalysis at industrial-level current densities

Seawater electroreduction is attractive for future H2 production and intermittent energy storage, which has been hindered by aggressive Mg2+/Ca2+ precipitation at cathodes and consequent poor stability. Here we present a vital microscopic bubble/precipitate traffic system (MBPTS) by constructing honeycomb-type 3D cathodes for robust anti-precipitation seawater reduction (SR), which massively/uniformly release small-sized H2 bubbles to almost every corner of the cathode to repel Mg2+/Ca2+ precipitates without a break. Noticeably, the optimal cathode with built-in MBPTS not only enables state-of-the-art alkaline SR performance (1000-h stable operation at -1 A cm-2) but also is highly specialized in catalytically splitting natural seawater into H2 with the greatest anti-precipitation ability. Low precipitation amounts after prolonged tests under large current densities reflect genuine efficacy by our MBPTS. Additionally, a flow-type electrolyzer based on our optimal cathode stably functions at industrially-relevant 500 mA cm-2 for 150 h in natural seawater while unwaveringly sustaining near-100% H2 Faradic efficiency. Note that the estimated price (~1.8 US$/kgH2) is even cheaper than the US Department of Energy's goal price (2 US$/kgH2).

Ampere-Level Current Density CO2 Reduction with High C2+ Selectivity on La(OH)3-Modified Cu Catalysts

The carbon dioxide reduction reaction (CO2RR) driven by electricity can transform CO2 into high-value multi-carbon (C2+) products. Copper (Cu)-based catalysts are efficient but suffer from low C2+ selectivity at high current densities. Here La(OH)3 in Cu catalyst is introduced to modify its electronic structure towards efficient CO2RR to C2+ products at ampere-level current densities. The La(OH)3/Cu catalyst has a remarkable C2+ Faradaic efficiency (FEC2+) of 71.2% which is 2.2 times that of the pure Cu catalyst at a current density of 1,000 mA cm-2 and keeps stable for 8 h. In situ spectroscopy and density functional theory calculations both show that La(OH)3 modifies the electronic structure of Cu. This modification favors *CO adsorption, subsequent hydrogenation, *CO─*COH coupling, and consequently increases C2+ selectivity. This work provides a guidance on facilitating C2+ product formation, and suppressing hydrogen evolution by La(OH)3 modification, enabling efficient CO2RR at ampere-level current densities.

Surface reconstruction in amorphous CoFe-based hydroxides/crystalline phosphide heterostructure for accelerated saline water electrolysis

Developing electrocatalysts with high activity and robust performance for large-scale seawater electrolysis to produce hydrogen holds immense significance. Herein, a highly active bifunctional electrode composed of amorphous cobalt-iron layered double hydroxides (CoFeLDH) and crystalline nickel phosphide (Ni2P) (denoted as CoFeLDH@Ni2P), is employed to boost hydrogen production through seawater electrolysis. The strong interface coupling effectively modifies the electronic structure at active sites, thereby accelerating the catalytic reaction kinetics. Impressively, in situ Raman and post-stability analyses demonstrate a unique reconstruction behavior on the CoFeLDH@Ni2P electrode. Bimetal co-incorporated NiOOH (CoFe-NiOOH) and Ni(OH)2 species are formed during the oxygen evolution reaction (OER), while CoFeLDH@Ni2P can transform into Ni(OH)2 species during the hydrogen evolution reaction (HER) process. Furthermore, the highly negatively charged surface selectively rejects Cl- ions by formed PO43-, endowing CoFeLDH@Ni2P with excellent tolerance and promising durability in saline electrolytes. Consequently, the CoFeLDH@Ni2P electrode exhibits an overpotential of 106 mV for HER at 10 mA cm-2 and 308 mV for OER to achieve 100 mA cm-2 in 1.0 M KOH solution. Additionally, the CoFeLDH@Ni2P(+,-) electrolyzer requires a low cell voltage of 1.56 V to deliver 10 mA cm-2 in 1.0 M KOH + Seasalt. This work presents an appealing strategy for the rational design of advanced electrocatalysts with amorphous-crystalline interfaces, which reveals the source of the activity of transition-metal phosphating compounds in saline water electrolysis.

Controlled Growth of Metal Atom Arrays on Graphdiyne for Seawater Oxidation

Advanced atomic-level heterointerface engineering provides a promising method for the preparation of next-generation catalysts. Traditional carbon-based heterointerface catalytic performance rely heavily on the undetermined defects in complex and demanding preparation processes, rendering it impossible to control the catalytic performance. Here, we present a general method for the controlled growth of metal atom arrays on graphdiyne (GDY/IrCuOx), and we are surprised to find strong heterointerface strains during the growth. We successfully controlled the thickness of GDY to regulate the heterointerface metal atoms and achieved compressive strain at the interface. Experimental and density functional theory calculation results show that the unique incomplete charge transfer between GDY and metal atoms leads to the formation of strong interactions and significant heterointerface compressive strain between GDY and IrCuOx, which results in high oxidation performances with 1000 mA cm-2 at a low overpotential of 283 mV and long-term stability at large current densities in alkaline simulated seawater. We anticipate that this finding will contribute to construction of high-performance heterogeneous interface structures, leading to the development of new generation of GDY-based heterojunction catalysts in the field of catalysis for future promising performance.

MXene-mediated reconfiguration induces robust nickel-iron catalysts for industrial-grade water oxidation

Nickel-iron oxy/hydroxides (NiFeOxHy) emerge as an attractive type of electrocatalysts for alkaline water oxidation reaction (WOR), but which encounter a huge challenge in stability, especially at industrial-grade large current density due to uncontrollable Fe leakage. Here, we tailor the Fe coordination by a MXene-mediated reconfiguration strategy for the resultant NiFeOxHy catalyst to alleviate Fe leakage and thus reinforce the WOR stability. The introduction of ultrafine MXene with surface dangling bonds in the electrochemical reconfiguration over Ni-Fe Prussian blue analogue induces the covalent hybridization of NiFeOxHy/MXene, which not only accelerates WOR kinetics but also improves Fe oxidation resistance against segregation. As a result, the NiFeOxHy coupled with MXene exhibits an extraordinary durability at ampere-level current density over 1,000 h for alkaline WOR with an ultralow overpotential of only 307 mV. This work provides a broad avenue and mechanistic insights for the development of nickel-iron catalysts toward industrial applications.

Organocatalyst Supported by a Single-Atom Support Accelerates both Electrodes used in the Chlor-Alkali Industry via Modification of Non-Covalent Interactions

Consuming one of the largest amount of electricity, the chlor-alkali industry supplies basic chemicals for society, which mainly consists of two reactions, hydrogen evolution (HER) and chlorine evolution reaction (CER). Till now, the state-of-the-art catalyst applied in this field is still the dimensional stable anode (DSA), which consumes a large amount of noble metal of Ru and Ir. It is thus necessary to develop new types of catalysts. In this study, an organocatalyst anchored on the single-atom support (SAS) is put forward. It exhibits high catalytic efficiency towards both HER and CER with an overpotential of 21 mV and 20 mV at 10 mA cm-2 . With this catalyst on both electrodes, the energy consumption is cut down by 1.2 % compared with the commercial system under industrial conditions. Based on this novel catalyst and the high activity, the mechanism of modifying non-covalent interaction is demonstrated to be reliable for the catalyst's design. This work not only provides efficient catalysts for the chlor-alkali industry but also points out that the SACs can also act as support, providing new twists for the development of SACs and organic molecules in the next step.

Diluting the Resistance of Built-in Electric Fields in Oxygen Vacancy-enriched Ru/NiMoO4-x for Enhanced Hydrogen Spillover in Alkaline Seawater Splitting

Recently, hydrogen spillover based binary (HSBB) catalysts have received widespread attention due to the sufficiently utilized reaction sites. However, the specific regulation mechanism of spillover intensity is still unclear. Herein, we have fabricated oxygen vacancies enriched Ru/NiMoO4-x to investigate the internal relationship between electron supply and mechanism of hydrogen spillover enhancement. The DFT calculations cooperate with in situ Raman spectrum to uncover that the H* spillover from NiMoO4-x to Ru. Meanwhile, oxygen vacancies weakened the electron supply from Ru to NiMoO4-x , which contributes to dilute the resistance of built-in electric field (BEF) for hydrogen spillover. In addition, the higher ion concentration in electrolyte will promote the H* adsorption step obviously, which is demonstrated by in situ EIS tests. As a result, the Ru/NiMoO4-x exhibits a low overpotential of 206 mV at 3.0 A cm-2 , a small Tafel slope of 28.8 mV dec-1 , and an excellent durability of 550 h at the current density of 0.5 A cm-2 for HER in 1.0 M KOH seawater.

Microzone-Acidification-Driven Degradation Mechanism of the NiFe-Based Anode in Seawater Electrolysis

The anode stability is critical for efficient and reliable seawater electrolyzers. Herein, a NiFe-based film catalyst was prepared by anodic oxidation to serve as a model electrode, which exhibited a satisfactory oxygen evolution performance in simulated alkaline seawater (1 M KOH + 0.5 M NaCl) with an overpotential of 348 mV at 100 mA cm-2 and a long-term stability of over 100 h. After that, the effects of the current density and bulk pH of the electrolyte on its stability were evaluated. It was found that the electrode stability was sensitive to electrolysis conditions, failing at 20 mA cm-2 in 0.1 M KOH + 0.5 M NaCl but over 500 mA cm-2 in 0.5 M KOH + 0.5 M NaCl. The electrode dissolved, and some precipitates immediately formed at the region very close to the electrode surface during the electrolysis. This can be ascribed to the pH difference between the electrode/electrolyte interface and the bulk electrolyte under anodic polarization. In other words, the microzone acidification accelerates the corrosion of the electrode by Cl-, thus affecting the electrode stability. The operational performances of the electrode under different electrolysis conditions were classified to further analyze the degradation behavior, which resulted in three regions corresponding to the stable oxygen evolution, violent dissolution-precipitation, and complete passivation processes, respectively. Thereby increasing the bulk pH could alleviate the microzone acidification and improve the stability of the anode at high current densities. Overall, this study provides new insights into understanding the degradation mechanism of NiFe-based catalysts and offers electrolyte engineering strategies for the application of anodes.

Metal nitrides for seawater electrolysis

Electrocatalytic high-throughput seawater electrolysis for hydrogen production is a promising green energy technology that offers possibilities for environmental and energy sustainability. However, large-scale application is limited by the complex composition of seawater, high concentration of Cl- leading to competing reaction, and severe corrosion of electrode materials. In recent years, extensive research has been conducted to address these challenges. Metal nitrides (MNs) with excellent chemical stability and catalytic properties have emerged as ideal electrocatalyst candidates. This review presents the electrode reactions and basic parameters of the seawater splitting process, and summarizes the types and selection principles of conductive substrates with critical analysis of the design principles for seawater electrocatalysts. The focus is on discussing the properties, synthesis, and design strategies of MN-based electrocatalysts. Finally, we provide an outlook for the future development of MNs in the high-throughput seawater electrolysis field and highlight key issues that require further research and optimization.

Ag Nanoparticle-Induced Surface Chloride Immobilization Strategy Enables Stable Seawater Electrolysis

Although hydrogen gas (H2 ) storage might enable offshore renewable energy to be stored at scale, the commercialization of technology for H2 generation by seawater electrolysis depends upon the development of methods that avoid the severe corrosion of anodes by chloride (Cl- ) ions. Here, it is revealed that the stability of an anode used for seawater splitting can be increased by more than an order of magnitude by loading Ag nanoparticles on the catalyst surface. In experiments, an optimized NiFe-layered double hydroxide (LDH)@Ag electrode displays stable operation at 400 mA cm-2 in alkaline saline electrolyte and seawater for over 5000 and 2500 h, respectively. The impressive long-term durability is more than 20 times that of an unmodified NiFe-LDH anode. Meticulous characterization and simulation reveals that in the presence of an applied electric field, free Cl- ions react with oxidized Ag nanoparticles to form stable AgCl species, giving rise to the formation of a Cl- -free layer near the anode surface. Because of its simplicity and effectiveness, it is anticipated that the proposed strategy to immobilize chloride ions on the surface of an anode has the potential to become a crucial technology to control corrosion during large-scale electrolysis of seawater to produce hydrogen.

Materials Design and System Innovation for Direct and Indirect Seawater Electrolysis

Green hydrogen production from renewably powered water electrolysis is considered as an ideal approach to decarbonizing the energy and industry sectors. Given the high-cost supply of ultra-high-purity water, as well as the mismatched distribution of water sources and renewable energies, combining seawater electrolysis with coastal solar/offshore wind power is attracting increasing interest for large-scale green hydrogen production. However, various impurities in seawater lead to corrosive and toxic halides, hydroxide precipitation, and physical blocking, which will significantly degrade catalysts, electrodes, and membranes, thus shortening the stable service life of electrolyzers. To accelerate the development of seawater electrolysis, it is crucial to widen the working potential gap between oxygen evolution and chlorine evolution reactions and develop flexible and highly efficient seawater purification technologies. In this review, we comprehensively discuss present challenges, research efforts, and design principles for direct/indirect seawater electrolysis from the aspects of materials engineering and system innovation. Further opportunities in developing efficient and stable catalysts, advanced membranes, and integrated electrolyzers are highlighted for green hydrogen production from both seawater and low-grade water sources.

Enhanced Metal-Support Interactions Boost the Electrocatalytic Water Splitting of Supported Ruthenium Nanoparticles on a Ni3 N/NiO Heterojunction at Industrial Current Density

Developing highly efficient and stable hydrogen production catalysts for electrochemical water splitting (EWS) at industrial current densities remains a great challenge. Herein, we proposed a heterostructure-induced-strategy to optimize the metal-support interaction (MSI) and the EWS activity of Ru-Ni3 N/NiO. Density functional theory (DFT) calculations firstly predicted that the Ni3 N/NiO-heterostructures can improve the structural stability, electronic distributions, and orbital coupling of Ru-Ni3 N/NiO compared to Ru-Ni3 N and Ru-NiO, which accordingly decreases energy barriers and increases the electroactivity for EWS. As a proof-of-concept, the Ru-Ni3 N/NiO catalyst with a 2D Ni3 N/NiO-heterostructures nanosheet array, uniformly dispersed Ru nanoparticles, and strong MSI, was successfully constructed in the experiment, which exhibited excellent HER and OER activity with overpotentials of 190 mV and 385 mV at 1000 mA cm-2 , respectively. Furthermore, the Ru-Ni3 N/NiO-based EWS device can realize an industrial current density (1000 mA cm-2 ) at 1.74 V and 1.80 V under alkaline pure water and seawater conditions, respectively. Additionally, it also achieves a high durability of 1000 h (@ 500 mA cm-2 ) in alkaline pure water.

Hydrogen co-production via nickel-gold electrocatalysis of water and formaldehyde

Hydrogen is one of the most promising future energy sources due to its highly efficient energy storage and carbon-free features. However, the energy input required for a hydrogen production protocol is an essential factor affecting its widespread adoption. Water electrolysis for hydrogen production currently serves a vital role in the industrial field, but the high overpotential of the oxygen evolution reaction (OER) dramatically impedes its practical application. The formaldehyde oxidation reaction (FOR) has emerged as a more thermodynamically favorable alternative, and the innovation of compatible electrodes may steer the direction of technological evolution. We have designed Au-Vo-NiO/CC as a catalyst that triggers the electrocatalytic oxidation of formaldehyde, efficiently producing H2 at the ultra-low potential of 0.47 V (vs. RHE) and maintaining long-term stability. Integrated with the cathodic hydrogen evolution reaction (HER), this bipolar H2 production protocol achieves a nearly 100% Faraday efficiency (FE).