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 Ni3N‐Co3N 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.
Sodium and potassium ions energy storage systems with low cost and high energy/power densities have recently drawn increasing interest as promising candidates for grid-level applications, while the lack of suitable anode materials with fast ion diffusion kinetics highly hinders their development. Herein, we develop a nanoscale confined in situ oxidation polymerization process followed by a conventional carbonization treatment to generate phosphorus and nitrogen dualdoped hollow carbon spheres (PNHCS), which can realize superior sodium and potassium ion storage performance. Importantly, the density functional theory calculation and combined characterizations, e.g., in situ Raman spectroscopy and ex situ X-ray photoelectron spectroscopy, decipher that the P/N doping can enhance the electronic transfer dynamics and ion adsorption capability, which are responsible for enhanced electrochemical performance. Inspiringly, the practicability of the PNHCS anode is demonstrated by assembling the potassium ion hybrid capacitors (KIHCs), where the prominent energy density is 178.80 Wh kg −1 at a power density of 197.65 W kg −1 , with excellent cycling stability, can be achieved. This work not only promotes the development of efficient anode material for sodium/potassium ion storage devices but also deciphers the embedded ion storage mechanism.
Designing highly active transition-metal-based electrocatalysts for energysaving electrochemical hydrogen evolution coupled with hydrazine oxidation possesses more economic prospects. However, the lack of bifunctional electrocatalysts and the absence of intrinsic structure−property relationship research consisting of adsorption configurations and dehydrogenation behavior of N 2 H 4 molecules still hinder the development. Now, a V-doped Ni 3 N nanosheet self-supported on Ni foam (V-Ni 3 N NS) is reported, which presents excellent bifunctional electrocatalytic performance toward both hydrazine oxidation reaction (HzOR) and hydrogen evolution reaction (HER). The resultant V-Ni 3 N NS achieves an ultralow working potential of 2 mV and a small overpotential of 70 mV at 10 mA cm −2 in alkaline solution for HzOR and HER, respectively. Density functional theory calculations reveal that the vanadium substitution could effectively modulate the electronic structure of Ni 3 N, therefore facilitating the adsorption/desorption behavior of H* for HER, as well as boosting the dehydrogenation kinetics for HzOR.
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