Substituting hydrazine oxidation reaction for oxygen evolution reaction can result in greatly reduced energy consumption for hydrogen production, however, the mechanism and the electrochemical utilization rate of hydrazine oxidation reaction remain ambiguous. Herein, a bimetallic and hetero-structured phosphide catalyst has been fabricated to catalyze both hydrazine oxidation and hydrogen evolution reactions, and a new reaction path of nitrogen-nitrogen single bond breakage has been proposed and confirmed in hydrazine oxidation reaction. The high electro-catalytic performance is attributed to the instantaneous recovery of metal phosphide active site by hydrazine and the lowered energy barrier, which enable the constructed electrolyzer using bimetallic phosphide catalyst at both sides to reach 500 mA cm−2 for hydrogen production at 0.498 V, and offer an enhanced hydrazine electrochemical utilization rate of 93%. Such an electrolyzer can be powered by a bimetallic phosphide anode-equipped direct hydrazine fuel cell, achieving self-powered hydrogen production at a rate of 19.6 mol h−1 m−2.

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.

AbstractWe report the development of a cobalt phosphide nanoarray as an efficient and stable catalyst for the hydrazine oxidation reaction (HzOR) in alkaline media. Its high hydrogen evolution reaction (HER) activity enables it to be used as a bifunctional catalyst for less energy‐intensive electrolytic hydrogen generation by replacing the sluggish oxygen evolution reaction with HzOR. The corresponding two‐electrode electrolyzer using such a nanoarray as both the anode for HzOR and the cathode for HER only needs a cell voltage of 0.2 V to drive 10 mA cm−2 in 1.0 M KOH with 100 mM hydrazine, which is 1.45 V less than that for pure water splitting. This electrolyzer also shows strong long‐term electrochemical durability with nearly 100 % faradic efficiency for hydrogen evolution.

In order to decrease the electricity consumption of water electrolysis, we investigated a novel hydrazine-assisted water electrolysis for electricity-independent hydrogen production, featuring with lower anodic hydrazine oxidation reaction (HzOR) than cathodic hydrogen evolution reaction (HER). The adsorption and semiconductor characteristics of hierarchical porous CoNS@CuPD, interlacing by Co(OH)2 nanosheets on the Cu dendrites surface, are selectively modified to optimize anodic HzOR and cathodic HER performance through doping B and P heteroatoms, respectively. The working potential of HzOR on B-doped CoNS@CuPD negatively shifts to − 146 mV at 10 mA cm−2, while that of HER on P-doped CoNS@CuPD positively shifts to − 70 mV. Consequently, the hydrazine electrolysis device using B-/P-doped catalysts output a small voltage of 60 mV at 10 mA cm−2, achieving co-generation of hydrogen and electricity for the first time. This work brings an intrinsic break in hydrogen-rich molecule-assisted water electrolysis for hydrogen production.

Hydrazine-assisted hydrogen evolution cell has been regarded as a promising route to replace conventional water splitting because of the lower thermodynamic oxidation potential. Therefore, the design and synthesis of highly efficient bifunctional electrocatalysts for anodic hydrazine oxidation reaction (HzOR) and cathodic hydrogen evolution reaction (HER) are crucial and highly desired. In this work, we report a facile synthesis strategy to prepare hollow CoSe2/MoSe2 nanospheres with abundant active interfaces for hydrazine-assisted hydrogen production. The homogeneous mixing of Co and Mo ions in the metal organic framework precursors ensures the formation of intimately contacted interfaces after selenization, leading to the “reinforced concrete” CoSe2/MoSe2 composites. Benefiting from the CoSe2/MoSe2 interfaces, the hollow CoSe2/MoSe2 nanosphere performs a low HER overpotential of 168 mV with an excellent stability over 12 h. Additionally, it also exhibits a low overpotential of 386 mV (vs. RHE) for HzOR and an ultralow cell voltage (1 mA cm−2) of 160 mV, which are among the best reported performance of powdered electrocatalysts. The present work develops a promising bifunctional electrocatalyst with active interfaces for energy-saving electrolytic hydrogen production.

Water splitting is a sustainable and clean hydrogen-production technology, but driven either by solar energy with natural intermittent, or by power grid with high cost, which is not conductive to sustainable development. Additionally, the sluggish anodic oxygen evolution reaction (OER) remains a huge obstacle for efficient hydrogen production. Herein, an intersected nanosheets decorating micro-walls structure nickel-cobalt phosphide grown on Ni foam electrode (NiCoP/NF) is prepared, and displays good hydrogen evolution reaction (HER), excellent hydrazine oxidation reaction (HzOR) and enhanced NiCoP/NF//Zn battery capacity performance. Based on the trifunctional NiCoP/NF electrode, a continuous solar-driven energy-saving hydrogen generation is constructed. The solar cells drive the efficient hydrogen production and hydrazine degradation plus simultaneously charge the NiCoP/NF//Zn battery during the day; then the charged NiCoP/NF//Zn battery provide high output voltage to drive hydrogen generation and hydrazine degradation at night. The continuous solar-driven energy-saving hydrogen generation plus sewage treatment strategy exhibits a new way for clean and sustainable energy supply plus curbing environmental pollution.

The application of proton exchange membrane water electrolyzer (PEMWE) technology has long been limited by the excessive energy consumption and poor catalyst durability because of the harsh corrosive and oxidative conditions that are related to the anodic oxygen evolution reaction (OER) in acidic electrolytes. Herein, we circumvent this challenge by adopting alternative hydrazine oxidation reaction (HzOR) as the anodic half-reaction, integrated with the cathodic hydrogen evolution reaction (HER) for sustainable hydrogen production. To this end, we further developed a PtCo alloy nanosheets electrocatalyst that can efficiently catalyze both the HzOR and HER with ultralow potentials. Specifically, the overall hydrazine splitting driven by the PtCo alloy requires only 0.28 V at 10 mA cm−2 along with outstanding stability of more than 3000 h. We further proposed a PEM hydrazine electrolyzer (PEMHE) design to promote the practical application. The device can not only produce hydrogen with a high yield rate of 1.87 mmol h−1 cm−2 at a practical current density of 100 mA cm−2 with a long durability of 60 h, but also effectively decontaminate hydrazine sewage with the hydrazine removal efficiency up to 100%. Our work provides a new solution to simultaneous mass hydrogen fuel production and hydrazine hazard removal from acidic waste water at minimized energy consumption.

Electrochemical water splitting for H2 production is limited by the sluggish anode oxygen evolution reaction (OER), thus using hydrazine oxidation reaction (HzOR) to replace OER has received great attention. Here we report the hierarchical porous nanosheet arrays with abundant Ni3 N-Co3 N heterointerfaces on Ni foam with superior hydrogen evolution reaction (HER) and HzOR activity, realizing working potentials of -43 and -88 mV for 10 mA cm-2 , respectively, and achieving an industry-level 1000 mA cm-2 at 200 mV for HzOR. The two-electrode overall hydrazine splitting (OHzS) electrolyzer requires the cell voltages of 0.071 and 0.76 V for 10 and 400 mA cm-2 , respectively. The H2 production powered by a direct hydrazine fuel cell (DHzFC) and a commercial solar cell are investigated to inspire future practical applications. DFT calculations decipher that heterointerfaces simultaneously optimize the hydrogen adsorption free energy (ΔGH* ) and promote the hydrazine dehydrogenation kinetics. This work provides a rationale for advanced bifunctional electrocatalysts, and propels the practical energy-saving H2 generation techniques.

Water splitting using renewable energy is a promising hydrogen production method without carbon emission. However, oxygen evolution reaction still suffers from its large overpotential and sluggish kinetics. Thus, alternative oxidation reactions rather than oxygen evolution reaction, such as ammonia, alcohols and hydrazine oxidation reaction are developed for hydrogen production. Rh is one of the most promising catalysts for electrochemical hydrazine splitting that can promote hydrogen evolution reaction on the cathode, which is a much more energy-saving way to generate hydrogen gas than water splitting. Unfortunately, Rh is also one of the most expensive novel metals on the market. Nevertheless, only a few studies have considered the amount of used Rh. In this study, the diffusion-restricted cation exchange (CE) process is suggested as an effective method to reduce the mass of inactive Rh for enhanced mass activity. By immersing the NiOOH substrate in the Rh3+ aqueous solution, Rh3+ atoms are easily exchanged with Ni3+ atoms in the NiOOH lattice on the surface, and the RhOOH forms on the outermost layer. Then, the RhOOH compounds are reduced into metallic rhodium by an electrochemical reduction process, resulting in fine Rh nanoparticles smaller than 2 nm. Due to the suppression of Rh aggregation, a doubled mass activity for electrocatalytic hydrazine oxidation reaction is attained compared to that of conventional electrodeposited Rh catalysts. As a result, the proposed CE-derived Rh catalyst shows stability over 36 hours under the two-electrode hydrazine splitting system.

AbstractWater electrolysis is a promising source of hydrogen; however, technological challenges remain. Intensive efforts have focused on developing highly efficient and earth‐abundant electrocatalysts for water splitting. An effective strategy is proposed, using a bifunctional tubular cobalt perselenide nanosheet electrode, in which the sluggish oxygen evolution reaction is substituted with anodic hydrazine oxidation so as to assist energy‐efficient hydrogen production. Specifically, this electrode produces a current density of 10 mA cm−2 at −84 mV for hydrogen evolution and −17 mV for hydrazine oxidation in 1.0 m KOH and 0.5 m hydrazine electrolyte. An ultralow cell voltage of only 164 mV is required to generate a current density of 10 mA cm−2 for 14 hours of stable water electrolysis.