The Study Of Piezotronic Effect On P-type ZnO Nanostruture Photoelectrode For Enhanced Photoelectrochemical Properties

The use of solar energy to produce hydrogen is one of the main methods to solve the energy crisis and environmental pollution.In recent years,people have paid attention to semiconductor photocatalytic technology using semiconductor materials as a catalyst to effectively solve environmental and energy problems.Among them,TiO2 and ZnO are widely used in the field of photoelectrode as a metal oxide semiconductor because of its great stability,safety and low cost.ZnO has a better electron mobility than TiO2,and its photogenerated electron-hole recombination rate is lower,which can more effectively improve the quantum efficiency of the photoelectrode.ZnO is a short-wavelength luminescent material,which has great potential in the field of optoelectronics.Therefore,in order to design and manufacture highly efficient ZnO-based LEDs and optoelectronic devices,the preparation of p-type and n-type ZnO is indispensable.Since ZnO is generally n-type conductivity,O2 is usually produced as a photoanode in a PEC system,and its use as a photocathode electrode for direct hydrogen production requires preparation of p-type ZnO.However,the research process of ZnO can be applied to industrial production is still relatively slow.One of the important reasons is that it is difficult to obtain stable and low-resistance p-type ZnO under the current conditions.For improving the photocatalytic performance,one of the important measures is to accelerate the effective separation of photogenerated electron-hole.The piezotronic effect on ZnO can provide a strong electric field to reduce the recombination rate of charges and enhance the photoelectrochemical(PEC)performance.In this paper,p-type ZnO nanowires(NWs)were prepared by hydrothermal method,and the piezotronic effect was achieved by applying strains to improve the PEC performance of the photoelectrodes.Firstly,the optimal conditions for preparing p-type ZnO NWs are determined by exploring the Sb doping amount and annealing conditions.When the Sb doping amount is 0.2%(0.2Sb/ZnO NWs),experiments show that ZnO NWs can achieve better optoelectronic properties than undoped ZnO NWs.After annealing(0.2Sb/ZnO-anneal NWs),the ZnO NWs photoelectrode can extend the absorption range to near 414 nm.And the Mott-Schottky plot shows that the as-prepared ZnO NWs are p-type conductivity semiconductor.Under standard simulated sunlight,the photocurrent density of 0.2Sb/ZnO-anneal NWs can reach-0.85 mA/cm2 at a bias of 0 VRHE,which is 3.3 times than that of 0.2Sb/ZnO NWs.The 0.2Sb/ZnO-anneal NWs show good stability.After storage for 6 months at room temperature,the photocurrent density changed slightly,while the p-type conductivity did not change.The Sb doping and annealing treatment can effectively reduce the interface charge transfer resistance,thereby improving the PEC performance.Secondly,the results calculated by the first principle show that the piezotronic constants of ZnO NWs after Sb doping increase correspondingly.Therefore,the as-prepared 0.2Sb/ZnO-armeal sample is used to apply different strains to compare the effects of piezotronic effect on PEC properties.It was found that the application of tensile strain can further improve the PEC performance of the photoelectrode.By applying 0.6%tensile strain,the photocurrent density of the 0.2Sb/ZnO-anneal photoelectrode reaches-1.08 mA/cm2,which is 27.4%higher than that of ZnO NWs without strains.In 1 hour,the amount of hydrogen production can reach 559.5 dmol/cm2,and the calculated Faradaic efficiency reaches 86.3%.The changes brought about by the piezotronic effect are stable and long?lasting,while the conductive properties of ZnO will not change.The piezotronic effect can provide an effective driving force for the separation of photogenerated carriers and enhancing PEC performance.