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Cation-tunable flower-like (NiₓFe₁₋ₓ)₂P@graphitized carbon films as ultra-stable electrocatalysts for overall water splitting in alkaline media

Zhao, Hongyang, Wang, Yanwei, Fang, Ling, Fu, Weiwei, Yang, Xiaohui, You, Shili, Luo, Ping, Zhang, Huijuan, Wang, Yu
Journal of materials chemistry A 2019 v.7 no.35 pp. 20357-20368
active sites, adsorption, anodes, carbon, catalysts, catalytic activity, cathodes, cost effectiveness, electric power, electrochemistry, electrolysis, encapsulation, energy, hydrogen, iron, nanoparticles, nickel, platinum, renewable energy sources, synergism
Electrocatalytic water splitting is a promising strategy for green and renewable energy development by transforming electrical energy into hydrogen energy. Herein, we report a series of flower-like electrocatalysts with cation-tunable (NiₓFe₁₋ₓ)₂P nanoparticles encapsulated by porous graphitized carbon films (GCs) via the combination of morphology control and component adjustment. By progressively tailoring the atomic ratios of Ni/Fe, the electronic structure and electrocatalytic activities of (NiₓFe₁₋ₓ)₂P can be intriguingly modified to achieve versatile catalytic behavior for both the HER and the OER. DFT calculations also validate that the (NiₓFe₁₋ₓ)₂P with an optimal atomic ratio of Ni/Fe can support the |ΔGH*| to be close to the optimum and decrease the adsorption energy for water, which can boost the water splitting. Meanwhile, anchoring the adjustable (NiₓFe₁₋ₓ)₂P nanoparticles into GC interlayers can endow these composites with more available active sites, excellent conductivity and enhanced stability. In fact, the combined synergistic effect of cation-tuned (NiₓFe₁₋ₓ)₂P nanoparticles and porous conductive GCs is the reason that these composites exhibit enhanced electrocatalytic activities, as illustrated by a low overpotential of 206 mV at j = 10 mA cm⁻² (256 mV at j = 50 mA cm⁻²) for the OER. Meanwhile, the bifunctional (Ni₀.₇₅Fe₀.₂₅)₂P@GCs, as both the cathode and anode of an electrolyzer, effectuates an ultra-small cell potential of 1.541 V at j = 10 mA cm⁻² (1.573 V at j = 20 mA cm⁻²) for 30 h during electrolysis of water, rivaling commercial IrO₂ and Pt/C catalysts. More importantly, this work can provide a way of fabricating cost-saving, component-tunable and high-efficiency bimetallic electrocatalysts for water splitting.