Preparation Of Heteroatom Doped Cobalt Phosphide Catalytic Materials And Its Application In Water Splitting

The problems of energy shortage and environmental pollution have yet to be fundamentally solved,and it is imperative to develop and utilize clean and renewable hydrogen energy.As a common hydrogen production technology,electrolyzed water can produce hydrogen at the cathode and oxygen at the anode.However,in the actual water electrolysis reaction,the required voltage value（1.8-2.0 V）is always higher than the theoretical voltage value（1.23 V）,and there are problems such as low energy conversion efficiency and large power loss.The reason is that there are too high reaction barriers and overpotentials during the reaction.Therefore,the development of a catalytic material that can reduce the overpotential of the water splitting reaction and improve the reaction efficiency plays a vital role in the field of hydrogen production by electrolysis of water.In recent years,the dual-function OWS catalyst that can catalyze the HER reaction and the OER reaction at the same time has attracted the attention of researchers.Although cobalt phosphide,as a common transition metal-based water electrolysis catalyst material,has certain electrolytic water catalytic activity,its performance is still far from precious metal catalysts and commercial applications.Through our research,we found that Mn（manganese）,V（vanadium）,and Cu（copper）are transition metal elements of the fourth period.They have the same number of electron layers and similar atomic sizes as Co（cobalt）,which is benefit the successful doping of heteroatoms.Therefore,in this work,three heteroatoms of Mn,V,and Cu were used for doping,and a series of heteroatom-doped cobalt phosphide nano-catalytic materials grown on carbon cloth was prepared by combining with hydrothermal phosphating method.According to the appearance morphology,crystal structure,and catalytic activity characterization test results,we found that heteroatom doping successfully adjusted the appearance morphology and crystal structure of nano-catalytic materials,and the electrochemically active surface area and catalytic active sites were also greatly improved.Promote.In addition,DFT theoretical calculations and high-magnification transmission test results show that the surface of doped nanomaterials also produces more lattice defects and distortions.These are potential active centers that help accelerate hydrogen adsorption and desorption,and ultimately make electrolysis.The catalytic activity of water is significantly increased,showing greater commercial and industrial application value.In the first part,a ternary cobalt-manganese-phosphorus(Co_0.8-Mn_0.2-P/CC)nano-catalytic material grown on carbon cloth was prepared by Mn doping.The SEM test results showed that it was an urchin-like nanowire array structure.The hydrogen evolution LSV polarization curve test results show that the urchin-like Co_0.8-Mn_0.2-P/CC catalytic material has excellent HER activity.In 0.5 M H₂SO₄ acidic electrolyte,only an initial overpotential of 55 m V is required to drive a current density of 10 m A cm^-2.Similarly,in 1 M KOH alkaline electrolyte,when a current density of 10 m A cm^-2 is reached,only an initial overpotential of 61 m V is required.In addition,the results of the CV accelerated cycle test and the i-t time current density test show that the urchin-like Co_0.8-Mn_0.2-P/CC catalytic material has strong stability.The excellent HER catalytic activity of Co_0.8-Mn_0.2-P/CC is attributed to its high electrochemically active surface area and the strong synergistic effect between Co and Mn.In the second part,a vanadium-doped cobalt phosphide nanomaterial（V-CoPNRs/CC）grown on a carbon cloth was prepared by V-doping,which is a bifunctional water electrolysis catalytic material with a nanorod arrays structure.In 1 M KOH alkaline electrolyte,the HER test results show that V-Co P NRs/CC only needs an initial overpotential of 63 m V to drive a current density of 10 m A cm^-2.In the OER test,when a current density of 10 m A cm^-2 is reached,only an initial overpotential of 222 m V is required.It is worth noting that when we use V-Co P NRs/CC as anode and cathode materials,low battery voltages of 1.491 V and 1.606 V are required to drive 10 m A cm^-2 in 1 M KOH alkaline electrolyte.And a current density of 50 m A cm^-2,indicating its outstanding overall water split reaction（OWS）catalytic activity.Secondly,in the CV cycle test of2000 and 5000 cycles and the i-t test of 40 h at a current density of 50 m A cm^-2,V-Co P NRs/CC can maintain their strong electrolytic water catalytic activity without any significant drop.Demonstrating its huge stability and large-scale application potential.In the third part,an okra-shaped hollow copper-doped cobalt phosphide bifunctional catalyst(Cu_0.15-Co P/CC)was prepared by Cu doping.As a catalyst material for electrolyzed water without precious metals,Cu_0.15-Co P/CC has excellent HER catalytic activity in 1 M KOH alkaline electrolyte,and only 13 m V of initial overpotential is required to drive 10 m A cm^-2 The current density is lower than that of Pt-based noble metal catalysts.For OER,the overpotential required to reach a current density of 10 m A cm^-2 is 225 m V.When okra-shaped hollow Cu_0.15-Co P/CC is used as both cathode and anode electrode materials for OWS catalytic reaction,only a low battery voltage of 1.487 V is required to drive a current density of 10 m A cm^-2.In addition,the CV accelerated cycle test and the 60 h i-t test performed at a current density of 50 m A cm^-2 confirmed the strong stability of Cu_0.15-Co P/CC.The calculation results of density functional theory（DFT）also further confirm that Cu doping can lead to the polarization of the local structure of nanomaterials and reduce the free energy of hydrogen adsorption at the interstitial position,which is a potential reason for the improvement of catalytic performance.