MnOx Film-Coated NiFe-LDH Nanosheets on Ni Foam as Selective Oxygen Evolution Electrocatalysts for Alkaline Seawater Oxidation

Hexafluorophosphate additive enables durable seawater oxidation at ampere-level current density

Direct seawater electrolysis at ampere-level current densities, powered by coastal/offshore renewables, is an attractive avenue for sustainable hydrogen production but is undermined by chloride-induced anode degradation. Here we demonstrate the use of hexafluorophosphate (PF₆⁻) as an electrolyte additive to overcome this limitation, achieving prolonged operation for over 5,000 hours at 1 A cm-2 and 2300 hours at 2 A cm-2 using NiFe layered double hydroxide (LDH) as anode. Together with the experimental findings, PF₆⁻ can intercalate into LDH interlayers and adsorb onto the electrode surface under an applied electric field, blocking Cl⁻ and stabilizing Fe to prevent segregation. The constant-potential molecular dynamics simulations further reveal the accumulation of high surface concentrations of PF6- on the electrode surface that can effectively exclude Cl-, mitigating corrosion. Our work showcases synchronous interlayer and surface engineering by single non-oxygen anion species to enable Cl- rejection and marks a crucial step forward in seawater electrolysis.

Zincate Ion Enables M(II)-Vacancy NiFe Layered Double Hydroxide for Stable Seawater Electrolysis at 3 A cm-2

Seawater electrolysis offers a sustainable route for hydrogen production. Operating at high current densities can improve the energy efficiency but requires anodes that can sustain high oxygen evolution reaction (OER) activity, selectivity, and stability against negative effects of Cl-. Herein, NiFeZn layered double hydroxide (NiFeZn-LDH) demonstrates remarkable OER performance, requiring only 220 mV overpotential to achieve 10 mA cm-2, and maintaining 100% selective seawater oxidation to oxygen for 500 h at an unprecedented current density of 3 A cm-2, with minimal degradation. Through comprehensive characterizations, it is found that the dissolution of the amphoteric Zn-site and the following formation of Zn2+ vacancies are key to the excellent OER activity. The free Zn2+ in electrolyte converts to Zn(OH)4 2- and adsorbs onto the electrode, facilitating the OH- nucleophilic attack by disrupting the hydrogen bond network at the electrochemical interface. Furthermore, the steric hindrance of Zn(OH)4 2- suppresses the Cl- competing adsorption, ensuring 100% OER selectivity and long-term stability. As a result, an industrial-scale electrolyzer with NiFeZn-LDH as the anode operates stably for over 700 h in a saturated NaCl electrolyte, consuming only 4.26 Nm-3 H2. This work demonstrates the feasibility of developing energy-efficient, highly stable seawater electrolyzers that outperform conventional water electrolyzers.

Self-Supported NiCo2S4@Ce-NiFe LDH/CeO2 Nanoarrays for Electrochemical Water Splitting

The design of high-performance OER catalysts is crucial for efficient electrochemical water splitting (EWS). Herein, a NiCo2S4@Ce-NiFe LDH/CeO2 heterostructure nanoarray electrocatalyst with abundant oxygen defect sites is reported. The introduction of Ce species activates the lattice oxygen in the oxyhydroxides, inducing the transformation of the catalytic mechanism toward the lattice oxygen oxidation mechanism (LOM) pathway, bypassing the thermodynamic limitation of the adsorbate evolution mechanism (AEM), and strengthening the intrinsic activity of the material. Moreover, the reversible transitions between different oxidation states of Ce species and the high oxygen storage capacity of CeO2 regulate the adsorption behavior of the reaction intermediates, allowing it to be easier for the material to enrich the oxygen-containing intermediates, thereby improving the adsorption kinetics. Accordingly, NiCo2S4@Ce-NiFe LDH/CeO2 exhibits remarkable OER performance (η50 = 226 mV, η100 = 244 mV) and brilliant stability. Additionally, the presence of the CeO2 protective layer inhibits the impact of Cl- and other pollutants in seawater, which enables NiCo2S4@Ce-NiFe LDH/CeO2 to perform satisfactorily in seawater electrolysis, as well. This study offers a fresh perspective on the design of defect-rich OER catalysts.

NiFe-based arrays with manganese dioxide enhance chloride blocking for durable alkaline seawater oxidation

Seawater splitting is increasingly recognized as a promising technique for hydrogen production, while the lack of good electrocatalysts and detrimental chlorine chemistry may hinder further development of this technology. Here, the interfacial engineering of manganese dioxide nanoparticles decorated on NiFe layered double hydroxide supported on nickel foam (MnO2@NiFe LDH/NF) is reported, which works as a robust catalyst for alkaline seawater oxidation. Density functional theory calculations and experiment findings reveal that MnO2@NiFe LDH/NF can selectively enrich OH- and repel Cl- in oxygen evolution reaction (OER). MnO2@NiFe LDH/NF attains a current density of 1000 mA cm-2 in alkaline seawater with an ultralow overpotential of only 313 mV. Furthermore, it can maintain stability at 1500 mA cm-2 over 600 h. Further phosphidation of MnO2@NiFe LDH/NF can create MnOx@NiFeP/NF used in efficient hydrogen evolution reaction. Moreover, an anion exchange membrane electrolyzer with MnO2@NiFe LDH/NF as the anode and MnOx@NiFeP/NF as the cathode was also capable of seawater splitting at 500 mA cm-2 for 100 h. This work offers light to develop effective and long-lasting electrocatalysts for seawater splitting.

Application of functional coatings in water electrolyzers and fuel cells

Hydrogen, a sustainable energy carrier, plays a pivotal role in decarbonizing various industrial sectors. Key devices such as water electrolyzers and fuel cells enable a sustainable hydrogen cycle by producing hydrogen using renewable energies and converting hydrogen into electricity. The efficiency of these devices is primarily determined by electrocatalysts and other critical components like membranes, gas diffusion layers and bipolar plates. The dynamic and complex triple-phase reactions as well as the corrosive operational environments in these devices present significant challenges in achieving optimal performance and durability. This review not only summarizes recent advances in functional coatings but also elucidates the underlying mechanisms by which coatings modulate interfacial interactions and mitigate degradation. We further propose a roadmap for designing next-generation multifunctional coatings, emphasizing their potential to bridge the gap between laboratory research and industrial applications.

Polycalmagite Coating Enables Long-Term Alkaline Seawater Oxidation Over NiFe Layered Double Hydroxide

Renewable energy-powered seawater electrolysis is a green and attractive technique for producing high-purity hydrogen. However, severe chlorideions (Cl-) and their derivatives tend to corrode anodic catalysts at ampere-level current densities and hinder the application of seawater-to-H2 systems. Herein, a polycalmagite (PCM)-coated NiFe layered double hydroxide is presented on Ni foam (NiFe LDH@PCM/NF) that exhibits exceptional stability in alkaline seawater. PCM not only acts as a conductive layer to reduce charge transfer resistance of the anodes but also as a polymer-based protective layer to inhibit Cl- adsorption and stabilize metal ions oxidation due to its own anions and strong adhesion, thereby increasing activity and stability during alkaline seawater. Thus, NiFe LDH@PCM/NF only needs a low overpotential of 364 mV to reach up to 1000 mA cm-2 and maintains operation for 500 h without activity degradation. Moreover, a minimal amount of hypochlorite can be detected in electrolyte after a 500-h stability test. This development affords a significant exploration in creating durable and efficient anodes, highlighting the importance of polymer coating toward anti-corrosion in alkaline seawater oxidation.

Poly(Acid Yellow 17)-Modified CoFe-Layered Double Hydroxide Achieves Long-Term Alkaline Seawater Oxidation

Seawater electrolysis powered by renewable energy is a promising technique for green hydrogen production. However, the high concentration of chloride ions (Cl-) and their derivatives in seawater can severely corrode the anode catalyst, significantly challenging the lifespan of electrolyzers. Herein, we present a poly(acid yellow 17) (PAY) layer-modified CoFe-layered double hydroxide nanoarrays on nickel foam (CoFe LDH@PAY/NF), which serves as an efficient and stable electrocatalyst for alkaline seawater oxidation (ASO). PAY layer functions as an electrically conductive layer, which significantly enhances the conductivity of CoFe LDH/NF and thus improves the catalytic activity of ASO. Moreover, the sulfonic acid groups of PAY create a negatively charged environment on the surface of CoFe LDH/NF, effectively repelling Cl-, while the chlorine atoms in PAY form a Cl--free protective layer on the surface. These two mechanisms work synergistically to stabilize the seawater electrolysis process. Electrochemical test data indicate that CoFe LDH@PAY/NF achieves a current density of 1000 mA cm-2 at just 336 mV for ASO. The CoFe LDH@PAY/NF demonstrated superb stability, exhibiting slight activity degradation after 800 h ASO under 1000 mA cm-2. This work provides important guidance for developing anode catalysts resistant to Cl- corrosion during the ASO process.

Transition Metal-Coordinated Polymer Achieves Stable Seawater Oxidation over NiFe Layered Double Hydroxide

Seawater electrolysis has emerged as a promising approach for the generation of hydrogen energy, but the production of deleterious chlorine derivatives (e.g., chloride and hypochlorite) presents a significant challenge due to the severe corrosion at the anode. Transition metal-coordinated polymers have garnered attention as promising electrocatalysts for alkaline seawater oxidation (ASO), attributed to their remarkable chlorine corrosion resistance, high conductivity, and facile synthesis. In this study, we employ an anodic oxidation-electrodeposition strategy to grow NiFe-polyaniline on NiFe layered double hydroxide supported on Ni foam (NiFe LDH@NiFe-PANI/NF) as a highly efficient catalyst for ASO. We demonstrate stable ASO at industrial-level current densities (j) by employing a synergistic strategy that integrates NiFe-PANI, which offers resistance to chlorine-induced corrosion, and molybdate, which effectively repels chloride anions. In alkaline seawater, NiFe LDH@NiFe-PANI/NF requires 380 mV to sustain a j of 1000 mA cm-2, and it exhibits continuous operation for 500 h at a j of 1000 mA cm-2. Besides, the anion-exchange membrane electrolyzer consisting of NiFe LDH@NiFe-PANI/NF requires a voltage of 2.16 V to drive 300 mA cm-2. Notably, it can operate stably for 120 h, highlighting its potential for sustainable energy applications.

MXene-Assisted NiFe sulfides for high-performance anion exchange membrane seawater electrolysis

Anion exchange membrane seawater electrolysis is vital for future large-scale green hydrogen production, however enduring a huge challenge that lacks high-stable oxygen evolution reaction electrocatalysts. Herein, we report a robust OER electrocatalyst for AEMSE by integrating MXene (Ti3C2) with NiFe sulfides ((Ni,Fe)S2@Ti3C2). The strong interaction between (Ni,Fe)S2 and Ti3C2 induces electron distribution to trigger lattice oxygen mechanism, improving the intrinsic activity, and particularly prohibits the dissolution of Fe species during OER process via the Ti-O-Fe bonding effectively, achieving notable stability. Furthermore, the good retention of sulfates and the abundant groups of Ti3C2 provide effective Cl- resistance. Accordingly, (Ni,Fe)S2@Ti3C2 achieves high OER activity (1.598 V@2 A cm-2) and long-term durability (1000 h) in seawater system. Furthermore, AEMSE with industrial current density (0.5 A cm-2) and durability (500 h) is achieved by (Ni,Fe)S2@Ti3C2 anode and Raney Ni cathode with electrolysis efficiency of 70% and energy consumption of 48.4 kWh kg-1 H2.

Promoting the Corrosion Resistance of Mo-FeCoP@MnOx/NF via Double Protection Mechanisms Toward Electrolysis of Seawater at Ampere-Level Current Density

Producing hydrogen via seawater electrolysis is pivotal for addressing both energy and environmental crises. An industrial-current-density electrocatalyst consisting of Mo-doped FeCoP nanorods decorated with MnOx nanosheets is elaborately designed and grows in situ on nickel foam forming hierarchical Mo-FeCoP@MnOx/NF (M-FCP@MnOx/NF) for seawater electrolysis. Density functional theory calculations demonstrate that MnOx species remarkably reduce the adsorption capacity of Cl-, which enhances the corrosion resistance and selectivity of M-FCP@MnOx/NF during seawater electrolysis. Moreover, incorporating high-valence Mo species forms a superficial electrostatic layer on electrocatalysts to repel Cl-. Owing to its enhanced double protection mechanism and unique self-healing characteristics, M-FCP@MnOx/NF requires overpotentials of only 209 mV (HER) and 270 mV (OER) to reach a current density of ≈1.0 A cm-2 and maintains stable operation over 120 h during alkaline electrolysis of seawater. The colorimetric analysis indicates negligible ClO- production post stability test, indicating that the OER selectivity approaches 100%.

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.

Ultrafast Room-Temperature Synthesis of Phosphate-Intercalated NiFe Layered Double Hydroxides for High-Performance Alkaline Seawater Oxidation

Quick and easy synthetic methods and highly efficient catalytic performance are equally important to anodic oxygen evolution reaction (OER) electrocatalysts for alkaline seawater electrolysis. Herein, we report a facile one-step route to in situ growing PO43- intercalated NiFe layered double hydroxides (NiFe-LDH) on Ni foam (denoted as NiFe-P/NF) by a room-temperature immersion for several minutes. This ultrafast approach transforms the NF surface into a rough PO43- intercalated NiFe-LDH overlayer, which demonstrates outstanding OER performance in both alkaline simulated and natural seawaters owing to good hydrophilic interface and the electrostatic repulsion of PO43- against Cl- anions. Density functional theory calculations reveal that the intercalated PO43- can not only promote electron transfer but also prevent Cl- from entering the interlayer and simultaneously inhibit the migration of Cl- over the NiFe-LDH surface. In alkaline simulated and natural seawater electrolytes, NiFe-P/NF needs low overpotentials of 248 and 298 mV to achieve a current density of 100 mA cm-2, respectively. NiFe-P/NF can stably run over 42 h in an alkaline high-salty electrolyte (1 M KOH + 2.5 M NaCl) at 250 mA cm-2, more than 70 times that of NiFe/NF (0.6 h), emphasizing the critical role of the intercalated PO43- anions on the excellent durability. This study offers a new strategy to modify commercial NF to prepare efficient and stable OER catalysts for seawater electrolysis.

High Performance of Mn2O3 Electrodes for Hydrogen Evolution Using Natural Bischofite Salt from Atacama Desert: A Novel Application for Solar Saline Water Splitting

Solar saline water splitting is a promising approach to sustainable hydrogen production, harnessing abundant solar energy and the availability of brine resources, especially in the Atacama Desert. Bischofite salt (MgCl2·6H2O) has garnered significant attention due to its wide range of industrial applications. Efficient hydrogen production in arid or hyper arid locations using bischofite solutions is a novel and revolutionary idea. This work studied the electrochemical performance of Mn2O3 electrodes using a superposition model based on mixed potential theory and evaluated the superficial performance of this electrode in contact with a 0.5 M bischofite salt solution focusing on the hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) that occur during saline water splitting. The application of the non-linear superposition model provides valuable electrochemical kinetic parameters that complement the understanding of Mn2O3, this being one of the novelties of this work.

Boron modification promoting electrochemical surface reconstruction of NiFe-LDH for efficient and stable freshwater/seawater oxidation catalysis

Transition metal-based electrocatalysts generally take place surface reconstruction in alkaline conditions, but little is known about how to improve the reconstruction to a highly active oxyhydroxide surface for an efficient and stable oxygen evolution reaction (OER). Herein, we develop a strategy to accelerate surface reconstruction by combining boron modification and cyclic voltammetry (CV) activation. Density functional theory calculations and in-situ/ex-situ characterizations indicate that both B-doping and electrochemical activation can reduce the energy barrier and contribute to the surface evolution into highly active oxyhydroxides. The formed oxyhydroxide active phase can tune the electronic configuration and boost the OER process. The reconstructed catalyst of CV-B-NiFe-LDH displays excellent alkaline OER performance in freshwater, simulated seawater, and natural seawater with low overpotentials at 100 mA cm-2 (η100: 219, 236, and 255 mV, respectively) and good durability. This catalyst also presents outstanding Cl- corrosion resistance in alkalized seawater electrolytes. The CV-B-NiFe-LDH||Pt/C electrolyzer reveals prominent performance for alkalized freshwater/seawater splitting. This study provides a guideline for developing advanced OER electrocatalysts by promoting surface reconstruction.

Unraveling the crucial contribution of additive chromate to efficient and stable alkaline seawater oxidation on Ni-based layered double hydroxides

Seawater electrolysis to generate hydrogen offers a clean, green, and sustainable solution for new energy. However, the catalytic activity and durability of anodic catalysts are plagued by the corrosion and competitive oxidation reactions of chloride in high concentrations. In this study, we find that the additive CrO42- anions in the electrolyte can not only promote the formation and stabilization of the metal oxyhydroxide active phase but also greatly mitigate the adverse effect of Cl- on the anode. Linear sweep voltammetry, accelerated corrosion experiments, corrosion polarization curves, and charge transfer resistance results indicate that the addition of CrO42- distinctly improves oxygen evolution reaction (OER) kinetics and corrosion resistance in alkaline seawater electrolytes. Especially, the introduction of CrO42- even in the highly concentrated NaCl (2.5 M) electrolyte prolongs the durability of NiFe-LDH to almost five times the case without CrO42-. Density functional theory calculations also reveal that the adsorption of CrO42- can tune the electronic configuration of active sites of metal oxyhydroxides, enhance conductivity, and optimize the intermediate adsorption energies. This anionic additive strategy can give a better enlightenment for the development of efficient and stable oxygen evolution reactions for seawater electrolysis.

In Situ Phase Separation-Induced Self-Healing Catalyst for Efficient Direct Seawater Electrolysis

Direct seawater electrolysis technology for sustainable hydrogen production has garnered significant attention, owing to its abundant resource supply and economic potential. However, the complex composition and high chloride concentration of seawater have hindered its practical implementation. In this study, we report an in situ-synthesized dual-phase electrocatalyst (HPS-NiMo), comprising an amorphous phosphide protective outer phase and a crystalline alloy inner phase with supplementary sulfur active sites, to improve the kinetics of direct seawater electrolysis. The HPS-NiMo exhibits long-term stability, remaining stable for periods exceeding 120 h at 200 mA cm-2; moreover, it lowers the required operating voltage to ∼1.8 V in natural seawater. The chlorine chemistry, corrosion during direct natural seawater electrolysis, and mechanism behind the high-performing catalysts are discussed. We also investigated the possibility of recovering the anode precipitates, which inevitably occurs during seawater electrolysis.

Bipolar Membrane Seawater Splitting for Hydrogen Production: A Review

The growing demand for clean energy has spurred the quest for sustainable alternatives to fossil fuels. Hydrogen has emerged as a promising candidate with its exceptional heating value and zero emissions upon combustion. However, conventional hydrogen production methods contribute to CO2 emissions, necessitating environmentally friendly alternatives. With its vast potential, seawater has garnered attention as a valuable resource for hydrogen production, especially in arid coastal regions with surplus renewable energy. Direct seawater electrolysis presents a viable option, although it faces challenges such as corrosion, competing reactions, and the presence of various impurities. To enhance the seawater electrolysis efficiency and overcome these challenges, researchers have turned to bipolar membranes (BPMs). These membranes create two distinct pH environments and selectively facilitate water dissociation by allowing the passage of protons and hydroxide ions, while acting as a barrier to cations and anions. Moreover, the presence of catalysts at the BPM junction or interface can further accelerate water dissociation. Alongside the thermodynamic potential, the efficiency of the system is significantly influenced by the water dissociation potential of BPMs. By exploiting these unique properties, BPMs offer a promising solution to improve the overall efficiency of seawater electrolysis processes. This paper reviews BPM electrolysis, including the water dissociation mechanism, recent advancements in BPM synthesis, and the challenges encountered in seawater electrolysis. Furthermore, it explores promising strategies to optimize the water dissociation reaction in BPMs, paving the way for sustainable hydrogen production from seawater.

Heterostructured MoO3 Anchored Defect-Rich NiFe-LDH/NF as a Robust Self-Supporting Electrocatalyst for Overall Water Splitting

The rational design of inexpensive metal electrocatalysts with exciting catalytic activity for overall water splitting (OWS) remains a significant challenge. Heterostructures of NiFe layered double hydroxides (NiFe-LDHs) with abundant oxygen defects and tunable electronic properties have garnered considerable attention. Here, a self-supporting heterostructured catalyst (named MoO3/NiFe-NF) is synthesized via a hydrothermal method to grow NiFe-LDH with oxygen vacancies (OV) in situ on inexpensive nickel foam (NF). Subsequently, MoO3 is anchored and grown on the surface of NiFe-LDH by electrodeposition. The obtained catalysts achieved outstanding oxygen/hydrogen evolution reaction (OER/HER, 212 mV/85 mV@10 mA cm-2) performance in 1 m KOH. Additionally, when MoO3/NiFe-NF is utilized as the cathode and anode in OWS, a current density of 10 mA cm-2 can be obtained as an ultralow battery voltage of 1.43 V, a significantly lower value compared to the commercial electrolyzer incorporating Pt/C and IrO2 electrode materials. Finally, density functional theory (DFT) calculations and advanced spectroscopy technology are conducted to reveal the effects of heterojunctions and OV on the internal electronic structure of the electrical catalysts. Mainly, the present study provides a novel tactic for the rational design of remarkable, low-cost NiFe-LDH electrocatalysts with heterostructures for OWS.

CoNiFe alloy nanoparticles encapsulated into nitrogen-doped carbon nanotubes toward superior electrocatalytic overall water splitting in alkaline freshwater/seawater under large-current density

Developing bifunctional catalysts for overall water splitting with high activity and durability at high current density remains a challenge. In an attempt to overcome this bottleneck, in this work, unique CoNiFe-layered double hydroxide nanoflowers are in situ grown on nickel-iron (NiFe) foam through a corrosive approach and following a chemical vapor deposition process to generate nitrogen-doped carbon nanotubes at the presence of melamine (CoNiFe@NCNTs). The coupling effects between various metal species act a key role in accelerating the reaction kinetics. Moreover, the in situ formed NCNTs also favor promoting electrocatalytic activity and stability. For oxygen evolution reaction it requires low overpotentials of 330 and 341 mV in 1M KOH and 1M KOH + seawater to drive 500 mA cm-2. Moreover, water electrolysis can be operated with CoNiFe@NCNTs as both anode and cathode with small voltages of 1.95 and 1.93 V to achieve 500 mA cm-2 in 1M KOH and 1M KOH + seawater, respectively.

Improved Electrochemical Alkaline Seawater Oxidation over Cobalt Carbonate Hydroxide Nanowire Array by Iron Doping

Constructing efficient and low-cost oxygen evolution reaction (OER) catalysts operating in seawater is essential for green hydrogen production but remains a great challenge. In this study, we report an iron doped cobalt carbonate hydroxide nanowire array on nickel foam (Fe-CoCH/NF) as a high-efficiency OER electrocatalyst. In alkaline seawater, such Fe-CoCH/NF demands an overpotential of 387 mV to drive 500 mA cm^-2, superior to that of CoCH/NF (597 mV). Moreover, it achieves excellent electrochemical and structural stability in alkaline seawater.

Improved Alkaline Seawater Splitting of NiS Nanosheets by Iron Doping

Seawater electrolysis driven by renewable electricity is deemed a promising and sustainable strategy for green hydrogen production, but it is still formidably challenging. Here, we report an iron-doped NiS nanosheet array on Ni foam (Fe-NiS/NF) as a high-performance and stable seawater splitting electrocatalyst. Such Fe-NiS/NF catalyst needs overpotentials of only 420 and 270 mV at 1000 mA cm^-2 for the oxygen evolution reaction and hydrogen evolution reaction in alkaline seawater, respectively. Furthermore, its two-electrode electrolyzer needs a cell voltage of 1.88 V for 1000 mA cm^-2 with 50 h of long-term electrochemical durability in alkaline seawater. Additionally, in situ electrochemical Raman and infrared spectroscopy were employed to detect the reconstitution process of NiOOH and the generation of oxygen intermediates under reaction conditions.

Phase Segregation in Cu0.5 Ni0.5 Alloy Boosting Urea-Assisted Hydrogen Production in Alkaline Media

Coupling urea oxidation reaction (UOR) and hydrogen evolution reaction (HER) is promising for energy-efficient hydrogen production. However, developing cheap and highly active bifunctional electrocatalysts for overall urea electrolysis remains challenging. In this work, a metastable Cu_0.5 Ni_0.5 alloy is synthesized by a one-step electrodeposition method. It only requires the potentials of 1.33 and -28 mV to obtain the current density of ±10 mA cm^-2 for UOR and HER, respectively. The metastable alloy is considered to be the main reason causing the above excellent performances. In the alkaline medium, the as-prepared Cu_0.5 Ni_0.5 alloy exhibits good stability for HER; and conversely, NiOOH species can be rapidly formed during the UOR due to the phase segregation of Cu_0.5 Ni_0.5 alloy. In particular, for the energy-saving hydrogen generation system coupled with HER and UOR, only 1.38 V of voltage is needed at 10 mA cm^-2 ; and at 100 mA cm^-2 , the voltage decreases by ≈305 mV compared with that of the routine water electrolysis system (HER || OER). Compared with some catalysts reported recently, the Cu_0.5 Ni_0.5 catalyst owns superior electrocatalytic activity and durability. Furthermore, this work provides a simple, mild, and rapid method for designing highly active bifunctional electrocatalysts toward urea-supporting overall water splitting.