Preparation And HER Performance Of Ni/P Doped Mo₂C@CFP Electrocatalyst

Hydrogen energy is considered to be the most ideal energy carrier due to its high efficiency and no pollution.The technology of electrocatalytic water splitting has been extensively studied because it can efficiently produce high purity hydrogen and oxygen without other pollutant emissions.However,at present,highly efficient electrocatalytic water splitting for the hydrogen evolution reaction（HER）mainly rely on expensive and rare platinum group noble metals,which will limit its large-scale industrial application.The transition metal molybdenum carbide（Mo₂C）has been explored as potential substitute for the HER due to its unique electronic structure,i.e.,the electronic structure of the Mo₂C d-band is similar to that of Pt,so it has the best H adsorption energy,while the poor conductivity and slow interfacial reaction kinetics of a single Mo₂C catalyst affected its performance.In this paper,we propose to using Ni-doped and P,Ni co-doped to improve the catalytic performance of Mo₂C.A series of nano Mo₂C based electrocatalysts were synthesized on the carbon fiber paper（CFP）substrate by molten salt synthesis（MSS）method,and their catalytic performance for HER were studied.The main research result are as follow:（1）Ni-Mo₂C_CB/CFP catalyst was synthesized on CFP with nickel（CB）as dopant,molybdenum（Mo）powder,carbon black（CB）and CFP as raw materials by MSS method in the molten salt system of Na Cl and KCl at 1000°C for 3 h.XRD,SEM,TEM and XPS were used to characterize phase and microstructure.The results showed that Mo₂C was formed on the surface of carbon fiber uniformly.In addition,its catalytic performance was also tested.The wrinkled Ni-Mo₂C_CB/CFP catalyst exhibits good catalytic performance under acidic conditions,with low overpotentials of 121.4 m V(at j=10 m A cm^-2)and a Tafel slope of 116.9 m V dec^-1.In addition,the catalyst can work stably for more than 10 h at a voltage of 167 m V.Compared with other as-prepared catalysts,it also found that the introduction of CB and Ni can not only refine the size of Mo₂C particles,but also improve HER performance of the Mo₂C/CFP catalyst.（2）By using nickel nitrate（Ni（NO₃）₂）and Ni as dopants respectively,using MoO₃,CB and CFP as raw materials to prepare different self-supporting catalysts on CFP substrate via MSS method.XRD,SEM,TEM and XPS were used to characterize phase and microstructure.The results showed that when doped with Ni,most of the products were micron sized particles,while when doped with Ni（NO₃）₂,most of the products were Nano-shaped.When the solubility of Ni（NO₃）₂ is 3 M,the prepared Mo₂C-3M/CFP catalyst has single crystal Ni and polycrystalline Mo₂C,and the product was a loose and porous nano-flower structure,which has a large specific surface area.It can provide enough catalytic active sites for HER,and the structure is conducive to the transport of charges.The prepared Mo₂C-3M/CFP nanoflower catalyst showed excellent HER performance under acidic conditions with low overpotentials of 56 mV(at j=10 mA cm^-2)and a Tafel slope(27.4 mV dec^-1)comparable to that of commercial Pt/C(25.8 mV dec^-1).The excellent performance surpasses most of the recently reported noble-metal-free electrocatalysts.In addition,the outstanding long-term durability of Mo₂C-3M/CFP is demonstrated by showing no obvious fluctuations during 35 h of continuous HER testing.At the same time,the DFT calculations revealed that the doping of Ni increased the d-electros of Mo around the Fermi-level and shifted down the d band center（ε_d）,so that the adsorbed hydrogen(H_ads)is easier to desorb from the catalyst surface,thus leading to an enhanced intrinsic catalytic activity for Ni doped Mo₂C based catalysts.（3）Based on the obtained nano-flower Mo₂C-3M/CFP catalyst,P doping was introduced.Mo₂C-3M/CFP catalyst was phosphatized with sodium hypophosphite（Na H₂PO₂）to prepare P-Mo₂C-3M catalyst.The catalyst showed better electrocatalytic performance for the HER than Mo₂C-3M catalyst under acidic and basic conditions.With the overpotential of 48 m V and 140.5 m V to achieve a current density of 10 mA cm^-2,respectively,and the Tafel slope of 33.3 m V dec^-1 and 50.7 m V dec^-1,respectively.In addition,the stability of the catalyst under acidic and alkaline conditions was also tested.It was found that the activity of the P-Mo₂C-3M catalyst decreased by about 40%after30 h durability testing under acidic electrolyte,while under alkaline electrolyte after 20 h durability test,the performance of the catalyst material hardly changed.