Active site recovery and N-N bond breakage during hydrazine oxidation boosting the electrochemical hydrogen production

Electrochemical Hydrogen Production Coupling with the Upgrading of Organic and Inorganic Chemicals

Electrocatalytic water splitting powered by renewable energy is a green and sustainable method for producing high-purity H2. However, in conventional water electrolysis, the anodic oxygen evolution reaction (OER) involves a four-electron transfer process with inherently sluggish kinetics, which severely limits the overall efficiency of water splitting. Recently, replacing OER with thermodynamically favorable oxidation reactions, coupled with the hydrogen evolution reaction, has garnered significant attention and achieved remarkable progress. This strategy not only offers a promising route for energy-saving H₂ production but also enables the simultaneous synthesis of high-value-added products or the removal of pollutants at the anode. Researchers successfully demonstrate the upgrading of numerous organic and inorganic alternatives through this approach. In this review, the latest advances in the coupling of electrocatalytic H2 production and the upgrading of organic and inorganic alternative chemicals are summarized. What's more, the optimization strategy of catalysts, structure-performance relationship, and catalytic mechanism of various reactions are well discussed in each part. Finally, the current challenges and future prospects in this field are outlined, aiming to inspire further innovative breakthroughs in this exciting area of research.

Electrocatalytic N-H bond transformations: a zero-carbon paradigm for sustainable energy storage and conversion

With the escalating challenges of environmental pollution and energy scarcity, the exploration of novel energy storage and conversion systems has become imperative. In contrast to traditional energy systems centered on C-H bonds, electrocatalytic energy systems based on N-H bonds offer a transformative approach by circumventing the limitations of carbon cycles and enabling a complete cycle from energy storage to conversion. This review comprehensively introduces the concept and advantages of zero-carbon energy systems based on electrocatalytic N-H bond formation and cleavage. We delve into the reaction mechanisms of key electrocatalytic processes within these systems, along with the development and applications of associated electrocatalysts. Finally, we discuss the development prospect and challenges of zero-carbon energy systems based on the N-H bond, which provides guidance for the application of clean energy storage and conversion.

Built-in Electric Field in Ru/CoP Bifunctional Electrocatalyst Enhances Hydrazine-Assisted Water Splitting

Electrocatalytic hydrazine-assisted water splitting, incorporating the hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR), offers a promising avenue for hydrogen production. Herein, a Ru/CoP heterostructure is introduced, which enhances bifunctional catalytic activity through interfacial interaction induced by the built-in electric field between Ru nanoparticles and CoP nanosheets. This interaction optimizes the adsorption of intermediates and facilitates improved HER performances by weakening the strong adsorption of active hydrogen species (*H) on Ru and enhancing *H coverage on CoP through hydrogen spillover. Additionally, this electron interaction promotes the adsorption of N2H4 and its subsequent dehydrogenation, vital for HzOR activity. The heterostructure's significant reduction in required potentials for both reactions underscores its efficiency and potential economic benefits over traditional systems. Furthermore, the study validates the feasibility of using this approach for practical applications in sustainable hydrogen production, emphasizing its lower operational costs and enhanced catalytic stability and activity. This work not only showcases the practical applications of Ru/CoP but also underscores the broader applicability of heterostructure strategy in designing efficient bifunctional electrocatalysts.

Transition metal-doped cobalt phosphide for efficient hydrazine oxidation: a density functional theory study

Hydrazine oxidation reaction (HzOR) provides a sustainable alternative to the sluggish oxygen evolution reaction (OER), with a low theoretical thermodynamic potential (-0.33 V vs. RHE). However, developing efficient non-precious-metal catalysts for HzOR remains challenging. Here, we employed density functional theory (DFT) simulations to systematically investigate the mechanism of transition metal atoms doping (Au, Cr, Fe, Mn, Mo, Ni, Pd, Pt) to boost the N-H bond cleavage in HzOR. Among the studied dopants, Cr and Mn exhibit exceptional catalytic activity, achieving ultralow ΔG for RDS of -0.02 eV (CoP-Cr) and 0.02 eV (CoP-Mn), significantly lower than the high-coordination cobalt sites on undoped CoP (0.11 eV). CoP-Cr aligns with descriptor-driven optimization, while CoP-Mn operates via dopant-induced charge redistribution. Furthermore, we identified the adsorption free energy of N-NH2 (ΔGad-N2H2-1) as a robust descriptor for catalytic activity in the reaction pathway involving distal configuration, showing strong correlations with ΔG of RDS. This work proposed a dual design strategy-descriptor-driven optimization (CoP-Cr) and charge-redistribution enhancement (CoP-Mn)-as a roadmap for developing earth-abundant, high-performance catalysts. These insights pave the way for advancing sustainable hydrogen production and environmental remediation technologies.

Nanofibrous Ru/SnO2 heterostructure as robust bifunctional electrocatalyst for high-performance overall hydrazine splitting and Zn-hydrazine battery

Water electrolysis represents a green and efficient strategy for hydrogen (H2) production. However, the four-electron transfer process involved in its anodic oxygen evolution reaction (OER) half-reaction restricts the H2 generation rate. Employing hydrazine oxidation reaction (HzOR) as a substitute for OER in H2 generation can dramatically reduce energy consumption. In this study, we have successfully fabricated a nanofibrous Ru/SnO2 heterostructure that demonstrates exceptional performance in both hydrogen evolution reaction (HER) and HzOR. The obtained catalyst requires only a small overpotential of 39 mV for HER and an incredibly low potential of -0.076 V vs. reversible hydrogen electrode (RHE) for HzOR to generate the current density of 10 mA cm-2. Furthermore, the two-electrode overall hydrazine splitting (OHzS) cell operates at working voltages of 0.026 V and 0.292 V for the current densities of 10 mA cm-1 and 100 mA cm-2, respectively, notably lower than the overall water splitting (OWS) process. Moreover, it delivers a H2 yield rate of 0.40 mmol h-1 at a voltage of 1.6 V, outperforming the OWS by 10 times. This study introduces a groundbreaking concept in the advancement of highly efficient bifunctional catalysts for HER and HzOR, carrying significant implications for tackling energy scarcity issues.

Cu-Co Dual Sites Tandem Synergistic Effect Boosting Neutral Low Concentration Nitrate Electroreduction to Ammonia

Electrochemical nitrate reduction reaction (NO3 -RR) has emerged as an alternative strategy for wastewater treatment and ammonia production in neutral low-concentration nitrate. However, the electrocatalyst faces the challenge of limited NO3 - distribution and deficient active hydrogen (Hads) on the catalyst surface resulting from the low concentration of NO3 - and the difficulty of water splitting under neutral conditions. Here, a Cu-Co dual sites tandem synergistic catalysis mechanism has been proposed by doping Cu into CoP to facilitate the adsorption and conversion of NO3 - on Cu and to accelerate the water splitting on CoP leading to the significantly high NO3 -RR performance. The designed Cu-CoP catalyst exhibits an ammonia yield of 7.65 mg h-1 cm-2 and a Faraday efficiency of 85.1% at -1.0 V under neutral low-concentration nitrate (10 m M), which is the highest ammonia yield in the reported data. In situ characterization and theoretical calculations confirm the tandem synergistic effect, in which the Cu site favors the adsorption and activation of NO3 - to form NO2 -, and concurrently modulates the electronic structure of the Co site with optimized Hads adsorption resulting in the significantly enhanced NO3 -RR at neutral low concentration nitrate.

3d-2p-5d Orbital Synergy in Electrocatalytic Hydrazine Oxidation Assisted Water Splitting with Industrial Scale Current Density

The hydrazine oxidation reaction (HzOR) is a promising alternative to the oxygen evolution reaction (OER) in electrolyzers due to its lower oxidation potential than water, which significantly reduces energy demands and enhances hydrogen production efficiency. Incorporating high-valent 5d metals into 3d metal hydroxides has shown great potential for enhancing water-splitting performance through strong 3d-2p-5d orbital interactions, improving charge transfer, intermediate adsorption, and reducing overpotentials. This study showcases an innovative approach to enhance the electrocatalytic performance of Co(OH)2 through the incorporation of a high-valent 5d metal, tungsten (W6+), using a straightforward electrochemical synthesis method. The incorporation of W6+ into Co(OH)2 led to significant Co3d-O2p-W5d orbital coupling, strengthening the electronic interactions between Co and W. The high-valent W6+ facilitated electron withdrawal from Co2+, promoting easier access to Co3+ sites enhancing the catalytic performance. The W-Co(OH)2 achieved a current density of 100 mA cm-2 at a potential of 1.00 V versus RHE for the HzOR, which is notably lower than the 1.54 V versus RHE required for the OER. In a two-electrode system, substituting OER with HzOR resulted in a significant reduction in cell voltage by 0.50 V.

Self-Powered Hydrogen Production via Laser-Coordinated NiCoPt Alloy Catalysts in an Integrated Zn-Hydrazine Battery with Hydrazine Splitting

This study proposes a novel approach for the rapid transformation of bimetallic NiCo-oxides into trimetallic NiCoPt alloys using a pulsed laser technique in an ethanol medium in the presence of Pt salts. The electrochemical results demonstrate the exceptional dual-functional activity of the optimized NiCoPt-10 alloy, effectively catalyzing both hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR). Specifically, the NiCoPt-10 alloy presents a low overpotential of 90 mV at 10 mA·cm-2 for HER and a small working potential of 0.068 V versus the reversible hydrogen electrode (RHE) at 10 mA·cm-2 for HzOR. In situ Raman spectroscopy and theoretical calculations delivered insights into the dual-functional activity of the NiCoPt alloy. Consequently, the overall hydrazine splitting (OHzS) electrolyzer, employing a NiCoPt-10||NiCoPt-10 configuration, required only 0.295 V to deliver 10 mA·cm-2. Notably, using this dual-functional NiCoPt-10 catalyst as the cathode combined with Zn foil as the anode in a Zn-hydrazine (Zn-Hz) battery, achieved efficient hydrogen (H2) production with an energy efficiency of 97%. Furthermore, self-powered H2 production is realized by integrating the Zn-Hz battery with the OHzS electrolyzer, demonstrating its excellent potential for practical applications. Thus, this rapid synthetic strategy can aid in designing effective electrocatalysts for addressing challenges in H2 energy production.

Self-Triggering a Locally Alkaline Microenvironment of Co4Fe6 for Highly Efficient Neutral Ammonia Electrosynthesis

Electrochemical nitrate reduction reaction (eNO3-RR) to ammonia (NH3) holds great promise for the green treatment of NO3- and ambient NH3 synthesis. Although Fe-based electrocatalysts have emerged as promising alternatives, their excellent eNO3-RR-to-NH3 activity is usually limited to harsh alkaline electrolytes or alloying noble metals with Fe in sustainable neutral electrolytes. Herein, we demonstrate an unusual self-triggering localized alkalinity of the Co4Fe6 electrocatalyst for efficient eNO3-RR-to-NH3 activity in neutral media, which breaks down the conventional pH-dependent kinetics restrictions and shows a 98.6% NH3 Faradaic efficiency (FE) and 99.9% NH3 selectivity at -0.69 V vs RHE. The synergetic Co-Fe dual sites were demonstrated to enable the optimal free energies of eNO3-RR-to-NH3 species and balance water dissociation and protonation of adsorbed NO2-. Notably, the Co4Fe6 electrocatalysts can attain a high current density of 100 mA cm-2 with a high NH3 FE surpassing 96% and long-term stability for over 500 h eNO3-RR-to-NH3 in a membrane electrode assembly (MEA) electrolyzer. This work provides insight into tailoring the self-reinforced local-alkalinity on the Fe-based alloy electrocatalysts for eNO3-RR-to-NH3 and thus avoids alkaline electrolytes and noble metals for practical sustainable nitrate upcycling technology.

High-Entropy Alloy Nanoflower Array Electrodes with Optimizable Reaction Pathways for Low-Voltage Hydrogen Production at Industrial-Grade Current Density

Developing sufficiently effective non-precious metal catalysts for large-current-density hydrogen production is highly significant but challenging, especially in low-voltage hydrogen production systems. Here, we innovatively report high-entropy alloy nanoflower array (HEANFA) electrodes with optimizable reaction pathways for hydrazine oxidation-assisted hydrogen production at industrial-grade current densities. Atomic-resolution structural analyses confirm the single-phase solid-solution structure of HEANFA. The HEANFA electrodes exhibit the top-level electrocatalytic performance for both the alkaline hydrogen evolution reaction (HER) and hydrazine oxidation reaction (HzOR). Furthermore, the hydrazine oxidation-assisted splitting (OHzS) system assembled with HEANFA as both anode and cathode exhibits a record-breaking performance for hydrogen production. It achieves ultralow working voltages of 0.003, 0.081, 0.260, 0.376, and 0.646 V for current densities of 10, 100, 500, 1 000, and 2 000 mA cm-2, respectively, and remarkable stability for 300 h, significantly outperforming those of previously reported OHzS systems and other chemicals-assisted hydrogen production systems. Theoretical calculations reveal that extraordinary performance of HEANFA for OHzS is attributed to its abundant high-activity sites and optimizable reaction pathways in HER and HzOR. In particular, HEANFA enables intelligent migration of key intermediates during HzOR, thereby optimizing the reaction pathways and creating high-activity sites, ultimately endowing the extraordinary performance for OHzS.

Partial oxidation of Rh/Ru nanoparticles within carbon nanofibers for high-efficiency hydrazine oxidation-assisted hydrogen generation

Hydrazine oxidation reaction (HzOR), an alternative to oxygen evolution reaction, effectively mitigates hydrazine pollution while achieving energy-efficient hydrogen production. Herein, partially oxidized Ru/Rh nanoparticles embedded in carbon nanofibers (CNFs) are fabricated as a bifunctional electrocatalyst for hydrogen evolution reaction (HER) and HzOR. The presence of multiple components including metallic Ru and Rh and their oxides provides numerous electrochemically active sites and superior charge transfer properties, thus improving the electrocatalytic performance. Additionally, the confinement of the active components within CNFs further enhances structural stability. Consequently, the optimized electrocatalyst exhibits ultralow overpotentials of 16 mV at 10 mA cm-2 and 176 mV to reach an industry-level current density of 1 A cm-2 for HER, considerably outperforming the benchmark Pt/C catalyst. Furthermore, it shows an outstanding anodic HzOR activity, achieving a small potential of -0.019 V to generate 10 mAcm-2. A two-electrode overall hydrazine splitting (OHzS) cell prepared using the electrocatalyst operates at a compelling voltage that is 1.953 V lower than that of the overall water splitting (OWS) cell at 200 mA cm-2. Furthermore, the OHzS cell achieves a hydrogen production rate of 1.17 mmol h-1, which is 15-fold that of OWS. Additionally, Rh1Ru1Ox-CNFs-350 is used to construct a Zn-hydrazine battery with excellent performance. This study presents an effective system for achieving high-yielding green H2 production with low energy consumption while simultaneously addressing hydrazine pollution.

Recent Advances and Perspectives on Coupled Water Electrolysis for Energy-Saving Hydrogen Production

Overall water splitting (OWS) to produce hydrogen has attracted large attention in recent years due to its ecological-friendliness and sustainability. However, the efficiency of OWS has been forced by the sluggish kinetics of the four-electron oxygen evolution reaction (OER). The replacement of OER by alternative electrooxidation of small molecules with more thermodynamically favorable potentials may fundamentally break the limitation and achieve hydrogen production with low energy consumption, which may also be accompanied by the production of more value-added chemicals than oxygen or by electrochemical degradation of pollutants. This review critically assesses the latest discoveries in the coupled electrooxidation of various small molecules with OWS, including alcohols, aldehydes, amides, urea, hydrazine, etc. Emphasis is placed on the corresponding electrocatalyst design and related reaction mechanisms (e.g., dual hydrogenation and N-N bond breaking of hydrazine and C═N bond regulation in urea splitting to inhibit hazardous NCO- and NO- productions, etc.), along with emerging alternative electrooxidation reactions (electrooxidation of tetrazoles, furazans, iodide, quinolines, ascorbic acid, sterol, trimethylamine, etc.). Some new decoupled electrolysis and self-powered systems are also discussed in detail. Finally, the potential challenges and prospects of coupled water electrolysis systems are highlighted to aid future research directions.

Triple Regulations via Fe Redox Boosting Nitrate Reduction to Ammonia at Industrial Current Densities

Electrochemical nitrate reduction reaction (NO3 -RR) has promising prospects for green synthesis of ammonia and environmental remediation. However, the performance of catalysts at high current density usually suffers from the high energy barrier for the nitrate (NO3 -) to nitrite (NO2 -) and the competitive hydrogen evolution. Herein, we proposed a two-step relay mechanism through spontaneous redox reaction followed electrochemical reaction by introducing low-valence Fe species into Ni2P nanosheets to significantly enhance the NO3 -RR performance at industrial current density. The existence of low-valence Fe species bypasses the NO3 - to NO2 - step through the spontaneous redox with NO3 - to produce NO2 - and Fe2O3, regulates the electronic structure of Ni2P to reduce the barrier of NO2 - to NH3, thirdly prohibits the hydrogen evolution by consuming the excess active hydrogen through reduction of Fe2O3 to recover low-valence Fe species. The triple regulations via Fe redox during the two-step relay reactions guarantee the Fe-Ni2P@NF high ammonia yield of 120.1 mg h-1 cm-2 with Faraday efficiency of more than 90% over a wide potential window and a long-term stability of more than 130 h at ~1000 mA cm-2. This work provides a new strategy to realize the design and synthesis of nitrate reduction electrocatalysts at high current densities.

Cocktail Effect of 4d/5d Band Twisted High-Entropy Alloys on Carbon Nanotube for Hydrazine Splitting

Herein, multi-walled carbon nanotubes (CNT) embedded with RuPdIrPtAu-high entropy alloys (HEA) via pulsed laser irradiation in liquids are successfully fabricated. The resultant composite synergistically enhances hydrazine oxidation reaction (HzOR)-boosted water electrolysis. Notably, HEA with ≈2-5 nm size, are uniformly distributed across the surface of the CNTs. An optimized HEA/CNT-10 demonstrates exceptional performance in oxygen and hydrogen evolution reactions (OER and HER), depicted by ultralow overpotentials of 30.7 and 330 mV at 10 mA cm-2, respectively. By replacing OER with HzOR, HEA/CNT-10 needs a lower potential of 0.1 V to accomplish 10 mA cm-2, as compared to OER (1.56 V vs. RHE). Moreover, the hydrazine splitting electrolyzer desirable a small voltage of 0.242 V to attain 10 mA cm-2, while maintaining exceptional stability. Experimental and DFT studies validate the cocktail effects and role of multiple metal-sites in HEA/CNT-10, which significantly enhance the efficiency of parallel HER||HzOR processes, highlighting its potential in energy-efficient, hydrogen production. In situ Raman probe indicated the configuration of an acidic environment, monitoring of H3O+, during HER, despite the basic conditions. This is attributed to the dominance of the Heyrovsky step, facilitated by the high catalytic activity of the HEA, coupled with protonation of the CNT surface.

Achieving Excess Hydrogen Output via Concurrent Electrochemical and Chemical Redox Reactions on P-Doped Co-Based Catalysts with Electron Manipulation and Kinetic Regulation

Electrolytic hydrogen production is of great significance in energy conversion and sustainable development. Traditional electrolytic water splitting confronts high anode voltage with oxygen generation and the amount of hydrogen produced at cathode depends entirely on the quantity of electric charge input. Herein, excess hydrogen output can be achieved by constructing a spontaneous hydrazine oxidation reaction (HzOR) coupled hydrogen evolution reaction (HER) system. For the hydrazine oxidation-assisted electrolyzer in this work, both the external input electrons and the electrons produced by spontaneous chemical redox reaction can reduce water, producing more hydrogen than traditional electrolytic water splitting system. The ultrafast kinetics of bifunctional P-doped Co-based catalysts plays a key role in the spontaneous feature of HzOR/HER redox reaction and low working voltage of hydrazine oxidation-assisted electrolyzer (12 mV@100 mA cm-2). Theoretical calculation results and ex situ/in situ spectra demonstrate that doped P could optimize electronic structure, regulate adsorption energy of intermediates, and thus endows catalysts with ultrafast kinetics. This work provides a new pathway for the development of spontaneous oxidation-assisted hydrogen production, to achieve excess hydrogen output via concurrent electrochemical and chemical redox reactions.

Electrodegradation of nitrogenous pollutants in sewage: from reaction fundamentals to energy valorization applications

The excessive accumulation of nitrogen pollutants (mainly nitrate, nitrite, ammonia nitrogen, hydrazine, and urea) in water bodies seriously disrupts the natural nitrogen cycle and poses a significant threat to human life and health. Electrolysis is considered a promising method to degrade these nitrogenous pollutants in sewage, with the advantages of high efficiency, wide generality, easy operability, retrievability, and environmental friendliness. For particular energy devices, including metal-nitrate batteries, direct fuel cells, and hybrid water electrolyzers, the realization of energy valorization from sewage purification processes (e.g., valuable chemical generation, electricity output, and hydrogen production) becomes feasible. Despite the progress in the research on pollutant electrodegradation, the development of electrocatalysts with high activity, stability, and selectivity for pollutant removal, coupled with corresponding energy devices, remains a challenge. This review comprehensively provides advanced insights into the electrodegradation processes of nitrogenous pollutants and relevant energy valorization strategies, focusing on the reaction mechanisms, activity descriptors, electrocatalyst design, and actuated electrodes and operation parameters of tailored energy conversion devices. A feasibility analysis of electrodegradation on real wastewater samples from the perspective of pollutant concentration, pollutant accumulation, and electrolyte effects is provided. Challenges and prospects for the future development of electrodegradation systems are also discussed in detail to bridge the gap between experimental trials and commercial applications.

Plasma-Constructed Co2P-Ni2P Heterointerface for Electro‑Upcycling of Polyethylene Terephthalate Plastic to Co-Produce Hydrogen and Formate

Integrating electrochemical upcycling of polyethylene-terephthalate (PET) and the hydrogen evolution reaction (HER) is an energy-saving approach for electrolytic hydrogen (H2) production, along with the coproduction of formate. Herein, a novel and rapid strategy of cold plasma phosphating is employed to synthesize Co2P-Ni2P heterointerface decorated on carbon cloth (Co2P-Ni2P/CC) to catalyze H2 generation and reform PET. Notably, the obtained Co2P-Ni2P/CC exhibits eminent ethylene glycol oxidation reaction (EGOR) and HER activities, effectuating low potentials of merely 1.300 and -0.112 V versus RHE at 100 mA cm-2 for the EGOR and HER, respectively, also attaining an ultralow cell bias of 1.300 V at 10 mA cm-2 for EG oxidation assisted-water splitting. DFT and characterization results validate that the as-formed built-in electric fields in the Co2P-Ni2P heterointerface can accelerate electrons transfer and deepen structural self-reconstruction, thereby boosting effectively water dissociation and ethylene glycol (EG) dehydrogenation. Impressively, coupling HER with PET-derived EG-to-formate in a flow-cell electrolyzer assembled with Co2P-Ni2P/CC pair achieves an intriguing formate Faradaic efficiency of 90.6% and an extraordinary stable operation of over 70 h at 100 mA cm-2. The work exemplifies a facile and effective strategy for synthesizing metal phosphides electrocatalysts with extraordinary performance toward H2 generation of water splitting and recycling of PET.

Quantum-sized CoP nanodots with rich vacancies: Enhanced hydrazine oxidation, hydrazine-assisted water splitting, and Zn-hydrazine battery performance through interface modulation

Reducing the size of catalysts and tuning their electronic structure and interfacial properties are key to enhancing catalytic performance. Herein, a series of quantum-sized Co-based nanodot composites, including Co3O4/C, CoS2/C, CoN/C, and CoP/C, were synthesized using chemical vapor deposition (CVD) methods. By means of experimental measurement and theoretical calculation, CoP/C exhibited more robust electrochemical response than other Co-based compounds in electrochemical oxidation of N2H4 (HzOR) and hydrogen evolution reaction (HER). The catalytic activities of CoP/C can be further enhanced by introducing Co vacancies on the surface of CoP/C (labeled as Co1-xP/C). The results demonstrated that Co1-xP/C not only exhibited notable electrochemical responses at an ultra-low N2H4 concentration of 0.67 μM, showcasing its potential for ultra-sensitive N2H4 detection but also realized HzOR instead of the oxygen evolution reaction (OER) half-reaction, thereby lowering the overpotential to 2.0 mV at 10.0 mA cm-2. Finally, a Zn-hydrazine (Zn-Hz) battery was fabricated as a promising energy conversion device, showing the exceptional practical value of Co1-xP/C.

Efficient Electrocatalytic Oxidation of Glycerol to Formate Coupled with Nitrate Reduction over Cu-Doped NiCo Alloy Supported on Nickel Foam

Electrooxidation of biomass-derived glycerol which is regarded as a main byproduct of industrial biodiesel production, is an innovative strategy to produce value-added chemicals, but currently showcases slow kinetics, limited Faraday efficiency, and unclear catalytic mechanism. Herein, we report high-efficiency electrooxidation of glycerol into formate via a Cu doped NiCo alloy catalyst supported on nickel foam (Cu-NiCo/NF) in a coupled system paired with nitrate reduction. The designed Cu-NiCo/NF delivers only 1.23 V vs. RHE at 10 mA cm-2, and a record Faraday efficiency of formate of 93.8 %. The superior performance is ascribed to the rapid generation of NiIII-OOH and CoIII-OOH species and favorable coupling of surface *O with reactive intermediates. Using Cu-NiCo/NF as a bifunctional catalyst, the coupled system synchronously produces NH3 and formate, showing 290 mV lower than the coupling of hydrogen evolution reaction, together with excellent long-term stability for up to 144 h. This work lays out new guidelines and reliable strategies from catalyst design to system coupling for biomass-derived electrochemical refinery.

CdS-based Schottky junctions for efficient visible light photocatalytic hydrogen evolution

Heterojunctions photocatalysts play a crucial role in achieving high solar-hydrogen conversion efficiency. In this work, we mainly focus on the charge transfer dynamics and pathways for sulfides-based Schottky junctions in the photocatalytic water splitting process to clarify the mechanism of heterostructures photocatalysis. Sulfides-based Schottky junctions (CdS/CoP and CdS/1T-MoS2) were successfully constructed for photocatalytic water splitting. Because of the higher work function of CdS than that of CoP and 1T-MoS2, the direction of the built-in electric field is from CoP or 1T-MoS2 to semiconductor. Therefore, CoP and 1T-MoS2 can act as electrons acceptors to accelerate the transfer of photo-generated electron on the surface of CdS, thus improving the charge utilization efficiency. Meanwhile, CoP and 1T-MoS2 as active sites can also promote the water dissociation and lower the H+ reduction overpotential, thus contributing to the excellent photocatalytic hydrogen production activity (23.59 mmol·h-1·g-1 and 1195.8 mol·h-1·g-1 for CdS/CoP and CdS/1T-MoS2).

Modulation of Charge Redistribution in Heterogeneous CoSe-Ni0.95Se Coupling with Ti3C2Tx MXene for Hydrazine-Assisted Water Splitting

Integrating abundant dual sites of hydrazine oxidation reaction (HzOR) and hydrogen evolution reaction (HER) into one catalyst is extremely urgent toward energy-saving H2 production. Herein, CoSe-Ni0.95Se heterostructure coupling with Ti3C2Tx MXene (CoSe-Ni0.95Se/MXene) is fabricated on nickel foam (NF) to enhance the catalytic performance. The heterogeneous CoSe-Ni0.95Se and MXene coupling effect can change the coordination of Ni and Co, resulting in adjusted interfacial electronic field and enhanced electron transfer from Ni0.95Se to CoSe especially near MXene surface. Also, the appearance of MXene can anchor more active sites, thereby abundant nucleophilic CoSe and electrophilic Ni0.95Se are formed induced by the charge redistribution, which can tailor d-band center, moderate *H adsorption free energy (∆GH *) and facilitate adsorption/desorption for hydrazine intermediates, contributing to much enhanced HER and HzOR performance. For example, the low potentials of -160.8 and 116.1 mV at 400 mA cm-2 are seen for HER and HzOR with long-term stability of 7 days. When assembled as overall hydrazine splitting (OHzS), a small cell voltage of 0.35 V to drive 100 mA cm-2 is obtained. Such concept of integrating abundant nucleophilic and electrophilic dual sites and regulating their d-band centers can offer in-depth understandings to design efficient bifunctional HER and HzOR electrocatalysts.

Cu-P@silica-CNT-based catalyst for effective electrolytic water splitting in an alkaline medium with hydrazine assistance

In this study, we prepared a potential catalyst as an electrode modifier for electrolytic water splitting. In the preparation step, the amine was decorated with copper-phosphorus. It was immobilized over the silica surface, and the surface was engineered using N-(3-(trimethoxysilyl) propyl)ethylenediamine for the synthesis of the catalysts (AS). The morphological and structural aspects of the catalyst (AFS-Cu-P) were determined using FE-SEM/EDAX, FTIR, elemental analysis, BET, TGA, and XPS. The catalyst's efficacy for the oxygen evolution reaction (OER) was assessed in an alkaline medium with and without hydrazine. The hydrazine oxidation reaction enhanced the sluggish OER and facilitated water splitting. Detailed electrochemical measurements confirmed an increase in the kinetics of the process and a reduction in the activation energy needed to complete the process. The Tafel slopes, charge transfer coefficients, exchange-specific current densities, apparent rate constants, and diffusion coefficients are provided along with their respective values. The results showed that the presence of Cu and CNT is crucial in the conversion process.

Unlocking Efficient Hydrogen Production: Nucleophilic Oxidation Reactions Coupled with Water Splitting

Electrocatalytic water splitting driven by sustainable energy is a clean and promising water-chemical fuel conversion technology for the production of high-purity green hydrogen. However, the sluggish kinetics of anodic oxygen evolution reaction (OER) pose challenges for large-scale hydrogen production, limiting its efficiency and safety. Recently, the anodic OER has been replaced by a nucleophilic oxidation reaction (NOR) with biomass as the substrate and coupled with a hydrogen evolution reaction (HER), which has attracted great interest. Anode NOR offers faster kinetics, generates high-value products, and reduces energy consumption. By coupling NOR with hydrogen evolution reaction, hydrogen production efficiency can be enhanced while yielding high-value oxidation products or degrading pollutants. Therefore, NOR-coupled HER hydrogen production is another new green electrolytic hydrogen production strategy after electrolytic water hydrogen production, which is of great significance for realizing sustainable energy development and global decarbonization. This review explores the potential of nucleophilic oxidation reactions as an alternative to OER and delves into NOR mechanisms, guiding future research in NOR-coupled hydrogen production. It assesses different NOR-coupled production methods, analyzing reaction pathways and catalyst effects. Furthermore, it evaluates the role of electrolyzers in industrialized NOR-coupled hydrogen production and discusses future prospects and challenges. This comprehensive review aims to advance efficient and economical large-scale hydrogen production.

Recent progress in energy-saving electrocatalytic hydrogen production via regulating the anodic oxidation reaction

Hydrogen energy with its advantages of high calorific value, renewable nature, and zero carbon emissions is considered an ideal candidate for clean energy in the future. The electrochemical decomposition of water, powered by renewable and clean energy sources, presents a sustainable and environmentally friendly approach to hydrogen production. However, the traditional electrochemical overall water-splitting reaction (OWSR) is limited by the anodic oxygen evolution reaction (OER) with sluggish kinetics. Although important advances have been made in efficient OER catalysts, the theoretical thermodynamic difficulty predetermines the inevitable large potential (1.23 V vs. RHE for the OER) and high energy consumption for the conventional water electrolysis to obtain H2. Besides, the generation of reactive oxygen species at high oxidation potentials can lead to equipment degradation and increase maintenance costs. Therefore, to address these challenges, thermodynamically favorable anodic oxidation reactions with lower oxidation potentials than the OER are used to couple with the cathodic hydrogen evolution reaction (HER) to construct new coupling hydrogen production systems. Meanwhile, a series of robust catalysts applied in these new coupled systems are exploited to improve the energy conversion efficiency of hydrogen production. Besides, the electrochemical neutralization energy (ENE) of the asymmetric electrolytes with a pH gradient can further promote the decrease in application voltage and energy consumption for hydrogen production. In this review, we aim to provide an overview of the advancements in electrochemical hydrogen production strategies with low energy consumption, including (1) the traditional electrochemical overall water splitting reaction (OWSR, HER-OER); (2) the small molecule sacrificial agent oxidation reaction (SAOR) and (3) the electrochemical oxidation synthesis reaction (EOSR) coupling with the HER (HER-SAOR, HER-EOSR), respectively; (4) regulating the pH gradient of the cathodic and anodic electrolytes. The operating principle, advantages, and the latest progress of these hydrogen production systems are analyzed in detail. In particular, the recent progress in the catalytic materials applied to these coupled systems and the corresponding catalytic mechanism are further discussed. Furthermore, we also provide a perspective on the potential challenges and future directions to foster advancements in electrocatalytic green sustainable hydrogen production.

Ruthenium Nanoclusters and Single Atoms on α-MoC/N-Doped Carbon Achieves Low-Input/Input-Free Hydrogen Evolution via Decoupled/Coupled Hydrazine Oxidation

The hydrazine oxidation-assisted H2 evolution method promises low-input and input-free hydrogen production. However, developing high-performance catalysts for hydrazine oxidation (HzOR) and hydrogen evolution (HER) is challenging. Here, we introduce a bifunctional electrocatalyst α-MoC/N-C/RuNSA, merging ruthenium (Ru) nanoclusters (NCs) and single atoms (SA) into cubic α-MoC nanoparticles-decorated N-doped carbon (α-MoC/N-C) nanowires, through electrodeposition. The composite showcases exceptional activity for both HzOR and HER, requiring -80 mV and -9 mV respectively to reach 10 mA cm-2. Theoretical and experimental insights confirm the importance of two Ru species for bifunctionality: NCs enhance the conductivity, and its coexistence with SA balances the H ad/desorption for HER and facilitates the initial dehydrogenation during the HzOR. In the overall hydrazine splitting (OHzS) system, α-MoC/N-C/RuNSA excels as both anode and cathode materials, achieving 10 mA cm-2 at just 64 mV. The zinc hydrazine (Zn-Hz) battery assembled with α-MoC/N-C/RuNSA cathode and Zn foil anode can exhibit 97.3 % energy efficiency, as well as temporary separation of hydrogen gas during the discharge process. Therefore, integrating Zn-Hz with OHzS system enables self-powered H2 evolution, even in hydrazine sewage. Overall, the amalgamation of NCs with SA achieves diverse catalytic activities for yielding multifold hydrogen gas through advanced cell-integrated-electrolyzer system.

Engineering interfacial sulfur migration in transition-metal sulfide enables low overpotential for durable hydrogen evolution in seawater

Hydrogen production from seawater remains challenging due to the deactivation of the hydrogen evolution reaction (HER) electrode under high current density. To overcome the activity-stability trade-offs in transition-metal sulfides, we propose a strategy to engineer sulfur migration by constructing a nickel-cobalt sulfides heterostructure with nitrogen-doped carbon shell encapsulation (CN@NiCoS) electrocatalyst. State-of-the-art ex situ/in situ characterizations and density functional theory calculations reveal the restructuring of the CN@NiCoS interface, clearly identifying dynamic sulfur migration. The NiCoS heterostructure stimulates sulfur migration by creating sulfur vacancies at the Ni3S2-Co9S8 heterointerface, while the migrated sulfur atoms are subsequently captured by the CN shell via strong C-S bond, preventing sulfide dissolution into alkaline electrolyte. Remarkably, the dynamically formed sulfur-doped CN shell and sulfur vacancies pairing sites significantly enhances HER activity by altering the d-band center near Fermi level, resulting in a low overpotential of 4.6 and 8 mV at 10 mA cm-2 in alkaline freshwater and seawater media, and long-term stability up to 1000 h. This work thus provides a guidance for the design of high-performance HER electrocatalyst by engineering interfacial atomic migration.

Enhanced H2 production assisted by anodic iodide oxidation using transparent tin oxide-based electrodes

In this work, the direct use of transparent conducting oxides (TCOs) as cost-efficient anodes for the iodide oxidation reaction (IOR) is explored. Energy-saving hydrogen production assisted by the IOR is demonstrated using a hybrid water electrolysis system with FTO as the anode and Pt-wire as the cathode. The hybrid system delivers 10 mA cm-2 at a cell voltage as low as 1.15 V with the faradaic efficiency for H2 found to be ∼91%. This study may open avenues for developing novel systems that integrate the IOR with other high-value reduction reactions.

Next-Generation Green Hydrogen: Progress and Perspective from Electricity, Catalyst to Electrolyte in Electrocatalytic Water Splitting

Green hydrogen from electrolysis of water has attracted widespread attention as a renewable power source. Among several hydrogen production methods, it has become the most promising technology. However, there is no large-scale renewable hydrogen production system currently that can compete with conventional fossil fuel hydrogen production. Renewable energy electrocatalytic water splitting is an ideal production technology with environmental cleanliness protection and good hydrogen purity, which meet the requirements of future development. This review summarizes and introduces the current status of hydrogen production by water splitting from three aspects: electricity, catalyst and electrolyte. In particular, the present situation and the latest progress of the key sources of power, catalytic materials and electrolyzers for electrocatalytic water splitting are introduced. Finally, the problems of hydrogen generation from electrolytic water splitting and directions of next-generation green hydrogen in the future are discussed and outlooked. It is expected that this review will have an important impact on the field of hydrogen production from water.

Single-Atom Iron Catalyst as an Advanced Redox Mediator for Anodic Oxidation of Organic Electrosynthesis

Homogeneous electrocatalysts can indirect oxidate the high overpotential substrates through single-electron transfer on the electrode surface, enabling efficient operation of organic electrosynthesis catalytic cycles. However, the problems of this chemistry still exist such as high dosage, difficult recovery, and low catalytic efficiency. Single-atom catalysts (SACs) exhibit high atom utilization and excellent catalytic activity, hold great promise in addressing the limitations of homogeneous catalysts. In view of this, we have employed Fe-SA@NC as an advanced redox mediator to try to change this situation. Fe-SA@NC was synthesized using an encapsulation-pyrolysis method, and it demonstrated remarkable performance as a redox mediator in a range of reported organic electrosynthesis reactions, and enabling the construction of various C-C/C-X bonds. Moreover, Fe-SA@NC demonstrated a great potential in exploring new synthetic method for organic electrosynthesis. We employed it to develop a new electro-oxidative ring-opening transformation of cyclopropyl amides. In this new reaction system, Fe-SA@NC showed good tolerance to drug molecules with complex structures, as well as enabling flow electrochemical syntheses and gram-scale transformations. This work highlights the great potential of SACs in organic electrosynthesis, thereby opening a new avenue in synthetic chemistry.

Synergetic Catalytic Effect between Ni and Co in Bimetallic Phosphide Boosting Hydrogen Evolution Reaction

The application of electrochemical hydrogen evolution reaction (HER) for renewable energy conversion contributes to the ultimate goal of a zero-carbon emission society. Metal phosphides have been considered as promising HER catalysts in the alkaline environment, which, unfortunately, is still limited owing to the weak adsorption of H* and easy dissolution during operation. Herein, a bimetallic NiCoP-2/NF phosphide is constructed on nickel foam (NF), requiring rather low overpotentials of 150 mV and 169 mV to meet the current densities of 500 and 1000 mA cm-2, respectively, and able to operate stably for 100 h without detectable activity decay. The excellent HER performance is obtained thanks to the synergetic catalytic effect between Ni and Co, among which Ni is introduced to enhance the intrinsic activity and Co increases the electrochemically active area. Meanwhile, the protection of the externally generated amorphous phosphorus oxide layer improves the stability of NiCoP/NF. An electrolyser using NiCoP-2/NF as both cathode and anode catalysts in an alkaline solution can produce hydrogen with low electric consumption (overpotential of 270 mV at 500 mA cm-2).

Bifunctional Electrocatalysts for Overall and Hybrid Water Splitting

Electrocatalytic water splitting driven by renewable electricity has been recognized as a promising approach for green hydrogen production. Different from conventional strategies in developing electrocatalysts for the two half-reactions of water splitting (e.g., the hydrogen and oxygen evolution reactions, HER and OER) separately, there has been a growing interest in designing and developing bifunctional electrocatalysts, which are able to catalyze both the HER and OER. In addition, considering the high overpotentials required for OER while limited value of the produced oxygen, there is another rapidly growing interest in exploring alternative oxidation reactions to replace OER for hybrid water splitting toward energy-efficient hydrogen generation. This Review begins with an introduction on the fundamental aspects of water splitting, followed by a thorough discussion on various physicochemical characterization techniques that are frequently employed in probing the active sites, with an emphasis on the reconstruction of bifunctional electrocatalysts during redox electrolysis. The design, synthesis, and performance of diverse bifunctional electrocatalysts based on noble metals, nonprecious metals, and metal-free nanocarbons, for overall water splitting in acidic and alkaline electrolytes, are thoroughly summarized and compared. Next, their application toward hybrid water splitting is also presented, wherein the alternative anodic reactions include sacrificing agents oxidation, pollutants oxidative degradation, and organics oxidative upgrading. Finally, a concise statement on the current challenges and future opportunities of bifunctional electrocatalysts for both overall and hybrid water splitting is presented in the hope of guiding future endeavors in the quest for energy-efficient and sustainable green hydrogen production.

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).

High biocompatible FITC-conjugated silica nanoparticles for cell labeling in both in vitro and in vivo models

Fluorescence nanosilica-based cell tracker has been explored and applied in cell biological research. However, the aggregation of these nanoparticles at physiological pH is still the main limitation. In this research, we introduced a novel fluorescence nano-based cell tracker suitable for application in live cells. The silica-coated fluorescein isothiocyanate isomer (FITC-SiO2) nanoparticles (NPs) were modified with carboxymethylsilanetriol disodium salt (FITC-SiO2-COOH), integrating the dianion form of FITC molecules. This nanosystem exhibited superior dispersion in aqueous solutions and effectively mitigated dye leakage. These labeled NPs displayed notable biocompatibility and minimal cytotoxicity in both in vitro and in vivo conditions. Significantly, the NPs did not have negative implications on cell migration or angiogenesis. They successfully penetrated primary fibroblasts, human umbilical vein endothelial cells and HeLa cells in both 2D and 3D cultures, with the fluorescence signal enduring for over 72 h. Furthermore, the NP signals were consistently observed in the developing gastrointestinal tract of live medaka fish larvae for extended periods during phases of subdued digestive activity, without manifesting any apparent acute toxicity. These results underscore the promising utility of FITC-SiO2-COOH NPs as advanced live cell trackers in biological research.

Hierarchical Ohmic Contact Interface Engineering for Efficient Hydrazine-Assisted Hydrogen Evolution Reaction

Hydrazine oxidation reaction coupled with hydrogen evolution reaction (HER) is an effective strategy to achieve low energy water splitting for hydrogen production. In order to realize the application of hydrazine-assisted HER system, researchers have been focusing on the development of electrocatalysts with integrated dual active sites, while the performance under high current density is still unsatisfying. In this work, hierarchical Ohmic contact interface engineering is designed and used as a bridge between the NiMo and Ni2 P heterojunction toward industrial current density applications, with the charge transfer impedance greatly eliminated via such a pathway with low energy barrier. As a proof-of-concept, the importance of charge redistribution and energy barrier at the Ohmic contact interface is investigated by significantly reducing the voltage of overall hydrazine splitting (OHzS) at high current density. Intriguingly, the NiMo/Ni2 P hierarchical Ohmic contact heterojunction can drive current densities of 100 and 500 mA cm-2 with only 181 and 343 mV cell voltage in the OHzS electrolyzer with high electrocatalytic stability. The proposed hierarchical Ohmic contact interface engineering paves new avenue for hydrogen production with low energy consumption.

Single-Atom Manganese-Catalyzed Oxygen Evolution Drives the Electrochemical Oxidation of Silane to Silanol

The oxygen evolution reaction (OER), characterized by a four-electron transfer kinetic process, represents a significant bottleneck in improving the efficiency of hydrogen production from water electrolysis. Consequently, extensive research efforts have been directed towards identifying single-atom electrocatalysts with exceptional OER performance. Despite the comprehensive understanding of the OER mechanism, its application to other valuable synthetic reactions has been limited. Herein, we leverage the MOOH intermediate, a key species in the Mn-N-C single-atom catalyst (Mn-SA@NC), which can be cyclically delivered in the OER. We exploit this intermediate' s capability to facilitate electrophilic transfer with silane, enabling efficient silane oxidation under electrochemical conditions. The SAC electrocatalytic system exhibits remarkable performance with catalyst loadings as low as 600 ppm and an exceptional turnover number of 9132. Furthermore, the catalytic method demonstrates stability under a 10 mmol flow chemistry setup. By serving as an OER electrocatalyst, the Mn-SA@NC drives the entire reaction, establishing a practical Mn SAC-catalyzed organic electrosynthesis system. This synthesis approach not only presents a promising avenue for the utilization of electrocatalytic OER but also highlights the potential of SACs as an attractive platform for organic electrosynthesis investigations.

Self-Powered Hydrogen Production with Improved Energy Efficiency via Polysulfides Redox

In the pursuit of efficient solar-driven electrocatalytic water splitting for hydrogen production, the intrinsic challenges posed by the sluggish kinetics of anodic oxygen evolution and intermittent sunlight have prompted the need for innovative energy systems. Here, we introduce an approach by coupling the polysulfides oxidation reaction with the hydrogen evolution reaction for energy-saving H2 production, which could be powered by an aqueous zinc-polysulfides battery to construct a self-powered energy system. This unusual hybrid water electrolyzer achieves 300 mA cm-2 at a low cell voltage of 1.14 V, saving electricity consumption by 100.4% from 5.47 to 2.73 kWh per m3 H2 compared to traditional overall water splitting. Benefiting from the favorable reaction kinetics of polysulfides oxidation/reduction, the aqueous zinc-polysulfides battery exhibits an energy efficiency of approximately 89% at 1.0 mA cm-2. Specially, the zinc-polysulfide battery effectively stores intermittent solar energy as chemical energy during light reaction by solar cells. Under an unassisted light reaction, the batteries could release energy to drive H2 production through a hybrid water electrolyzer for uninterrupted hydrogen production. Therefore, the aim of simultaneously generating H2 and eliminating the restrictions of intermittent sunlight is realized by combining the merits of polysulfides redox, an aqueous metal-polysulfide battery, and solar cells. We believe that this concept and utilization of polysulfides redox will inspire further fascinating attempts for the development of sustainable energy via electrocatalytic reactions.

Lattice Strain Engineering of Ni2 P Enables Efficient Catalytic Hydrazine Oxidation-Assisted Hydrogen Production

Hydrazine-assisted water electrolysis provides new opportunities to enable energy-saving hydrogen production while solving the issue of hydrazine pollution. Here, the synthesis of compressively strained Ni2 P as a bifunctional electrocatalyst for boosting both the anodic hydrazine oxidation reaction (HzOR) and cathodic hydrogen evolution reaction (HER) is reported. Different from a multistep synthetic method that induces lattice strain by creating core-shell structures, a facile strategy is developed to tune the strain of Ni2 P via dual-cation co-doping. The obtained Ni2 P with a compressive strain of -3.62% exhibits significantly enhanced activity for both the HzOR and HER than counterparts with tensile strain and without strain. Consequently, the optimized Ni2 P delivers current densities of 10 and 100 mA cm-2 at small cell voltages of 0.16 and 0.39 V for hydrazine-assisted water electrolysis, respectively. Density functional theory (DFT) calculations reveal that the compressive strain promotes water dissociation and concurrently tunes the adsorption strength of hydrogen intermediates, thereby facilitating the HER process on Ni2 P. As for the HzOR, the compressive strain reduces the energy barrier of the potential-determining step for the dehydrogenation of *N2 H4 to *N2 H3 . Clearly, this work paves a facile pathway to the synthesis of lattice-strained electrocatalysts via the dual-cation co-doping.

Replacing Oxygen Evolution with Hydrazine Borane Oxidation for Energy-Saving Electrochemical Hydrogen Production

Electrochemical water splitting is a green strategy for hydrogen (H₂) production but is severely hindered by the sluggish anodic oxygen evolution reaction (OER). Therefore, replacing the sluggish anodic OER with more favorable oxidation reactions is an energy-saving approach for hydrogen production. Hydrazine borane (HB, N₂H₄BH₃) is considered a potential hydrogen storage material due to its easy preparation, nontoxicity, and high chemical stability. Furthermore, the complete electrooxidation of HB has a unique characteristic of a much lower potential compared to that of OER. All these make it an ideal alternative for energy-saving electrochemical hydrogen production, however, which has never been reported so far. Herein, HB oxidation (HBOR)-assisted overall water splitting (OWS) is proposed for the first time for energy-saving electrochemical hydrogen production. The as-synthesized NiCoP@CoFeP nanoneedle array catalyst exhibited superefficient OER, hydrogen evolution reaction (HER), and HBOR performance. Impressively, NiCoP@CoFeP serves as both anodic and cathodic electrocatalysts for HB-assisted OWS, only requires a low cell voltage of only 0.078 V to achieve a current density of 10 mA cm^-2, which was 1.4 V lower than that for HB-free OWS, indicating the highly energy-saving H₂ production.