Design And Construction Of High Efficient WP Self-supporting Electrodes Toward Hydrogen Evolution Reaction

Hydrogen energy with high energy density is a good substitute for fossil energy,and there are many advantages in the use of hydrogen as a fuel in fuel cells.Hydrogen produced by electrolysis of water is a reliable way to produce zero-pollution energy carrier,so lots of attention was paid to it.However,in the process of water splitting,hydrogen evolution reaction?HER?needs a large overpotential which leads to excessive energy waste to overcome this overpotential in electrolysis of water.Thus,we need to use the catalyst to reduce the overpotential to avoid this waste of energy.In commercial production process,electrolyte in HER is usually an acid solution or an alkaline solution.Te electrolyzer is easy corroded because of the acid electrolyte.So in earlier times,alkaline electrolyte is more usual,while the net structure of Ni-series metal or alloy and low-carbon steel which plated nickel is used as working electrode,but its hydrogen production efficiency is low,and can not be produced on a large scale.Since 60s of this century,the acidic electrolytic cell?PEM?system come into sight,the biggest difference between the alkaline electrolytic cell and PEM is that the intermediate equipment segregate cathode from anode is the proton exchange membrane,which allow proton in acidic medium passing through freely,and separating the hydrogen from the oxygen better to get higher purity hydrogen.W as an important transition metal,which its oxide,phosphides,sulfide is more stable in acidic electrolyte compared to most non-noble metal.In order to improve the stability of the catalyst electrode in acidic solution and ensure the efficiency of hydrogen evolution in electrode,this paper mainly studies the application of self-supporting electrode of W series transition metal applied in the HER.It mainly contains the following two parts:?1?We introduced a method in synthesis of WP on W foils simply by heat treatment and constructed coral nanostructure array at the same time.The In-situ synthesis method reduced the loss of catalysts and improved the conductivity during its work.And the catalytic activity of the WP in HER was further enhanced.We found in acidic and alkaline condition,the catalyst electrode exhibits higher catalytic activity than that of other WPx ever reported(When current density reached 10 mA.cm^-2,overpotential is only 109 mV in acidic solution;133 mV in alkaline solution).And the Faraday efficiency is close to 100%.In addition,coral like WP on W foil electrodes show very small Tafel slope(79.8 mV.dec^-1 in acid solution;70.1 mV.dec^-1in alkaline solution).The report simplifies the complexity of the nanostructures,and provides another way for the design of self-supporting transition metal compounds.?2?WO₃ nanowire arrays were grown on tungsten foil by improved KBr-coating oxidation method.Then,with hydrothermal sulfuration and gaseous phosphorus doping,phosphorus doped tungsten sulfide/tungsten oxide heterojunction nanowire arrays was formed.Through the addition of phosphorus,the electronic structure of WS2-WO3 was made more beneficial to HER.Compared with the previous chapter,we have not synthesized phosphides,but doped phosphorus.In phosphating process,the PH₃ will be decomposed to generate phosphorus and hydrogen when the temperature was above500 degrees,phosphorus may exist in the form of white phosphorus under high temperature which make it more danger for experiments process.In this chapter,we protected phosphorus source from high temperatures.which can make the process more safe while saving energy.Under acidic conditions,the initial overpotential of phosphide doped tungsten sulfide/tungsten oxide heterojunction nanowire arrays is as low as 95mV,and when the current density reaches 10 mA.cm^-2.The over potential of hydrogen evolution is only 156 mV.