Design Of Nanoporous Nickel-based Multi-element Alloy And Its Mechanism Of Hydrogen Production From Water Electrolysi

Hydrogen energy has the advantages of high heating value and zero pollution,and it is a very promising source of clean energy.Hydrogen production by water electrolysis has the advantages of high purity of hydrogen production,nonpolluting products,wide and easy availability of raw materials,and a simple preparation process.It has great advantages in low-carbon hydrogen production.Electrolyzed water consists of hydrogen and oxygen evolution reactions.Each process requires additional energy consumption,making the required decomposition voltage much higher than the theoretical value,resulting in very high energy consumption.Developing high-efficiency catalysts to accelerate the reaction kinetics might be the only way to reduce the energy consumption of water electrolysis.In this study,a series of integrated nanoporous Ni-based multielement alloy catalysts were designed and synthesized by alloying-dealloying,optimize its performance by adjusting the alloy composition and structure,and reveal the catalytic mechanism.The details are as follows:（1）The effects of Co and Mo doping on the structure and properties of nanoporous NiFeMn alloy catalysts were systematically studied.Mo doping caused the alloy to undergo spinodal decomposition,forming a heterogeneous junction structure in which the molybdenum-poor and molybdenum-rich regions were intertwined.During the dealloying process,the molybdenum-rich region had a stable structure,whereas the molybdenum-poor region formed nano pores by dealloying;Co doping will form a uniform single-phase alloy,and a uniform nanoporous structure will be formed after dealloying.The catalytic activity of the nanoporous NiFeMoMn alloy electrode with two phases was significantly higher than that of the nanoporous NiCoFeMn alloy electrode with single phase,and the existence of the Mo-rich area enhanced the structural stability of the material and avoided the collapse of the pore structure after long-term operation at a high current density.（2）Using the two-phase stable structure caused by spinodal decomposition,nanoporous NiCoFeMoMn high entropy alloy electrode was further designed for hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.The nanoporous high-entropy alloy electrode had a structure of multilevel pore channels,exposing more active sites to participate in the reaction,and it was conducive to the entry of the electrolyte and a rapid release of gas.In the HER,the overpotential was only 150 m V at a current density of 1,000 m A cm^–2.In fully electrolyzed water,only 1.47 V cell voltage was required.It reached a stable current density of 10 m A cm^–2 and worked continuously and stably for more than 375 h.（3）In order to further improve its catalytic activity,the effects of trace doping of noble metal Ir on the structure and OER properties of nanoporous high entropy alloy were systematically studied.The amount of Ir doping changed the number of precipitated phases in the alloy and at the same time changed the interplanar spacing of the electrode.The nanoporous Ir_0.5NiCoFeMoMn high-entropy alloy electrode had the best OER performance.At a current density of 10 m A cm^-2,the overpotential was only 218 m V,and it circulated stably for nearly 300 h at a current density of 100 m A cm^-2.（4）The catalytic nature of nano porous Ni based alloy was revealed by first principle calculation.The results show that doping Mn,Fe,Mo elements reduced the d band center of the surface atoms of the Ni-based multielement alloy,which weakened the bonding strength of H and the active site.At the same time,the doping of elements adjusted the electronic structure,improved the adsorption capacity of hydrogen intermediates,and provided the best hydrogen adsorption site.The synergistic effect between the element segregation and nonsegregation zones in the alloy further enhanced the activity of the catalyst.