Synthesis Of Highly-efficient Cobalt-based Phosphides For Electrocatalysis

Fossil energy has been the most important energy in the world for centuries,which has played a pivotal role in the development of global industry and technology.Even if fossil energy such as coal and natural gas can meet the world’s energy demands in the foreseeable future,the excessive exploitation and insufficient combustion of fossil energy have prompted people to seek cleaner and renewable alternative energy.Compared with other energy sources,hydrogen has a higher energy density,and the consumption product is only pollution-free water.Electrochemical water-spitting is a sustainable and efficient strategy to produce hydrogen,which has great potential in large-scale industrial applications.However,extra overpotential is needed to drive the hydrogen evolution reaction due to polarization of the electeode,which means that electrolysis always demands more energy.Exploring efficient electrocatalysts to reduce the overpotential for promoting electrochemical water-spitting is a key point to solve the challenge of excessive energy consumption.Transition metal phosphides have been regarded as promising electrocatalytic materials for hydrogen evolution,which possess pretty free energy of hydrogen adsorption in the hydrogen evolution reaction.Moreover,it has plenty of advantages such as good chemical stability,low cost,and environmental friendliness.However,its development is limited by its inferior electrical conductivity,less active sites and high agglomeration seriously.With the aim of soloving the above problems,the study demonstrates the design and construction of some novel cobalt-based phosphides through construction of heterostructures,coupling with conductive carbon materials,and construction of self-supporting catalytic electrode.The main study includes the following several contents.1.Mott-Schottky electrocatalysts Co/Co₂P@C microspheres were synthesized via gradual phosphorization strategy.By adjusting the ratio of the metallic Co and semiconductive Co₂P content,the optimized Co/Co₂P@C microspheres exhibit pretty HER propertie especially in alkaline electrolyte(10 m A cm^-2 at 158 m V).Moreover,the excellent electrocatalytic durability is proved by the stable reaction for 48h.The favorable catalytic property can be ascribed to the following factors（i）the increase of electron transfer at the heterojunction,（ii）synergy effect of dual electrocatalyst,（iii）porous carbon shell with great conductivity and stability.2.Carbon nanotubes always possess large specific surface area and high conductivity.The precursor was prepared by coupling Co-Ni PBA with CNT.Then,Co₂P/Ni₂P/CNT was fabricated from the precursor Co-Ni PBA via phosphorization.The coupled carbon nanotubes can effectively improve the conductivity,increase the active sites,and reduce the overpotential of the hydrogen evolution reaction of the the composite meterial.Co₂P/Ni₂P/CNT prefoms well as HER electrocalalyst,which reachs a current density of 10 m A cm^-2 at the overpotential of 151 m V in acidic electroyte and 202 m V in alkaline electrolyte,respectively,and showed catalytic stability for 48 h.The excellent HER ormance of Co₂P/Ni₂P/CNT can be ascribed to the following factors（i）excellent electrocatalytic potential of bimetallic phosphides,（ii）composited CNTs accelerate the electron transfer rate（iii）increase in specific surface area and corresponding increase in electrochemically active sites.3.The precursor-cobalt hydroxide nanosheet was fabricated on the carbon fiber paper by electrodeposition method,then the precursor was phosphated into Co₂P@CFP at high temperature and used as an electrocatalytic self-supporting electrode.Since the self-supporting electrode Co₂P@CFP avoids the use of polymer binder,the electron transport performance is significantly improved.The catalyst loading on the surface of the carbon fiber paper can be adjusted by controlling the time of deposition.The optimal Co₂P@CFP exhibits excellent HER properties,which achieve a current density of 10m A cm^-2 at the overpotential of 75 m V in acidic electrolyte and 77 m V in alkaline electrolyte,respectively.Moreover,The optimal Co₂P@CFP reachs a current density of10 m A cm^-2 at the overpotential of 360 m V for OER in alkaline electrolyte.Moreover,Co₂P@CFP is employed as the anode and cathode of the two-electrode electrolyzer to drive the total decomposition of water with an electrolysis voltage of 1.59 V to reach a current density of 10 m A cm^-2,which also shows great electrocatalytic stability for 40h.The excellent electrocatalytic performance of Co₂P@CFP can be ascribed to the following factors（i）improved electron transfer rate of the self-supporting electrode,（ii）increase in electrochemically active sites,（iii）electrocatalytic stability due to steady loading of electrocatalyst.