Modification Of Nickel-Cobalt Phosphide Catalysts And Their Catalytic Performance For Water-Splitting

Hydrogen energy is the cornerstone of all types of clean energy conversion and an ideal energy source for achieving carbon neutrality.Electrolytic water splitting is one of the effective ways to achieve large-scale industrial hydrogen production.The key to reducing the cost of electrolytic water splitting is developing highly active catalysts with a low activation energy of water decomposition.Ni and Co phosphides have been one of the hotspots in the research of electrocatalysts for water splitting.The synergistic effect between Ni and Co makes ternary Nickel-Cobalt phosphide more active than binary cobalt or nickel phosphide.However,Ni-Co phosphides differ significantly in hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）activity due to different substrates,compositions,and structures.There is still considerable room for improving catalytic performance.Therefore,this paper focuses on Ni-Co phosphides to further enhance the performance of electrolytic water splitting by compositing carbon materials and heteroatom doping modification,respectively.The main research objectives are as follows.（1）A series of Ni-Co phosphides with different atomic ratios of Ni and Co atoms were prepared.The effects of the atomic ratio of Ni and Co on the morphology,elemental composition,crystal structure,and catalytic performance for electrolytic water-splitting were investigated.The experimental results show that the Ni Co P catalyst prepared with a Ni:Co atomic ratio of 1:1 has the best catalytic activity for HER and OER.（2）A substrate with a 3D network structure was designed by loading nitrogen-doped carbon nanofibers on carbon fiber paper（NCCP）,on which a self-supporting petal-like Ni Co P electrocatalyst（Ni Co P/NCCP）with the optimum atomic ratio of Ni and Co was prepared.The HER activity of Ni Co P/NCCP in an acidic environment is comparable to that of a 20%Pt/C electrode,exhibiting excellent stability and requiring an overpotential of only 55 m V at a current density of 10 m A cm^-2.In an alkaline environment,an overpotential of only 260 m V is required to drive the current density of 10 m A cm^-2 for OER.The asymmetric electrolyzer using Ni Co P/NCCP as a bifunctional catalyst requires an ultra-low cell voltage of 1.04 V to achieve a current density of 10 m A cm^-2 and exhibits good stability.（3）A series of self-supporting nanowire arrays electrocatalysts with different B doping amounts on nickel foam substrates（y B-Ni Co P/NF）were designed and in situ prepared.The effect of B doping amount on the microstructure of the catalysts and the catalytic performance of water electrolysis were investigated.DFT calculations confirmed that B doping optimized the electronic structure of Ni Co P and Gibbs free energy of hydrogen adsorption(ΔG_H*),enhancing the intrinsic HER catalytic activity of the catalysts.The experimental results show that the10B-Ni Co P/NF requires an HER overpotential of 159 m V and an OER overpotential of 300 m V to reach a current density of 100 m A cm^-2 in an alkaline environment.The overall water-splitting electrolyzer assembled using 10B-Ni Co P/NF as the bifunctional electrode requires a cell voltage of 1.51 V to reach a current density of 10 m A cm^-2,outperforming the 20%Pt-C@NF‖Ir O₂@NF.（4）The self-supported N-Ni Co P/NF,Se-Ni Co P/NF,and S-Ni Co P/NF catalytic with the same doping amount of non-metallic elements N,S and Se were prepared by the controlled variable method.The experimental results indicate that the S-Ni Co P/NF electrode exhibits the best HER performance,with an overpotential of 137 m V at a high current density of 100 m A cm^-2,which is 41 m V less than that of the Ni Co P/NF electrode It also exhibits excellent long-term stability after continuous HER for 120 hours.The anion exchange membrane electrolysis device,which uses the S-Ni Co P/NF electrode as the catalytic layer,can operate stably in the temperature range of 25-70°C.This suggests that the S-Ni Co P/NF electrode has potential for use in AEM electrolyzer.