Controlled Synthesis Of Cobalt-based Phosphide And Their Electrocatalytic Oxygen Evolution Exploration

Hydrogen energy is an economical,efficient and environmentally friendly renewable energy,which is an ideal alternative to fossil fuels.Hydrogen production by electrolysis of water is the most promising and clean method for producing hydrogen fuel.However,the slow kinetics of anodic oxygen evolution reaction（OER）largely limits the development of hydrogen production by electrolysis of water.Precious metal catalysts with high performance in OER,such as RuO₂ and IrO₂,have been developed.However,their applications in industry are limited by cost and scarcity.At present,a variety of effective-cost and high efficiency non-noble metal electrocatalysts have been developed.Transition metal phosphates have attracted extensive attention for their excellent catalytic activity and stability among various non-noble metal catalysts.In this paper,two kinds of transition metal phosphates,Mn-CoP and Fe-CoP NSs,were synthesized as efficient OER electrocatalysts.Specific as follows:（1）Inspired by the hierarchical structure and atomic doping strategy,we synthesized Mn-doped CoP microspheres assembled from porous nanosheets as an efficient electrocatalyst for OER.Firstly,Mn-Co-EG hierarchical microspheres were synthesized by solvothermal method,and then CoMn₂O₄ porous hierarchical microspheres were obtained by calcination at high temperature in air in a tubular furnace.Finally,Mn-CoP was obtained by chemical vapor deposition（CVD）phosphating.The crystal phase,chemical composition and valence electron states of elements of the catalyst were investigated by XRD,XPS,ICP,et al.Then the structural characteristics of the catalyst were observed by TEM,SEM and HRTEM.In addition,the BET was performed to test the specific surface area and pore size distribution of the catalyst.Finally,the OER property of Mn-CoP in 1 M KOH electrolyte was evaluated by electrochemical test.It was found that Mn-CoP only required 285 m V overpotential and 34 m V dec^-1 Tafel slope to drive the current density of 10 m A cm^-2,both far exceeding the activity of commercial RuO₂(330 m V and 65 m V dec^-1).Besides,Mn-CoP exhibited excellent stability through3000 cycles of CV test and 50 h of chronoamperometry test.（2）Inspired by the advantages of two-dimensional nanosheet structure and atomic doping strategy,we synthesized Fe-CoP nanosheets（Fe-CoP NSs）with rich defects,which exhibited excellent OER activity.Firstly,ZIF-67 NSs was synthesized by solvothermal method.Then,by using Lewis’s acid etching,ZIF-67 was treated with FeCl₂ethanol solution to obtain Fe-ZIF-67 NSs with cross-like channels on the surface.Subsequently,Annealed and oxidized in air to Fe-Co₃O₄ NSs.And finally,Fe-CoP NSs was obtained by CVD phosphating.After synthesis,TEM,HRTEM and SEM were used to observe the internal fine structure and external morphology of the catalyst.Besides,XRD,XPS,ICP and EDS were used to test the crystal phase,chemical composition and electronic valence state of the catalyst.And the OER activity of the catalyst was evaluated by electrochemical test.It is demonstrated that Fe-CoP NSS have outstanding OER performance,with overpotential and Tafel slope of 312 m V and 56.1 m V dec^-1 at current density of 10 m A cm^-2,which outperforming than that of precious metal catalyst RuO₂(344 m V and 62.4 m V dec^-1).In addition,after 2000 CV cycles and 20 h chronoamperometry tests,the property of Fe-CoP NSs exhibited almost no attenuation,showing good stability and durability.In conclusion,this paper provides an effective strategy for the synthesis of efficient and stable transition metal phosphide OER electrocatalyst.