The Regulation Of Cocatalyst For BiVO₄ Photoanode With Enhanced Photoelectrocatalytic Activity Towards Oxygen Evolution

In recent years,the coordination of rare earth metals with metal oxide/hydroxide electrocatalysts（eg,Ni,Fe,Co-based）has attracted widespread attention in the field of oxygen evolution reaction（OER）.Although these types of electrocatalysts show excellent OER activity,the semiconductors supported by cocatalysts still face the issue about insufficient photoelectrochemical（PEC）water splitting performance.Therefore,designing highly active co-catalysts decorated on semiconductors to achieve effective PEC water oxidation remains a challenge.The main research contents and results are as follows:（1）NiFe layered double hydroxide was synthesized by hydrothermal method and grown on the BiVO₄ photoanode in situ.Compared with BiVO₄ photoanode,NiFe LDH can significantly improve the oxygen production activity of the photoanode.Under the irradiation of AM 1.5G(100mW cm^-2)and 1.23 V _RHE,the photocurrent density of NiFe LDH/BiVO₄ can reach 3.2 mA·cm^-2 when NiFe LDH is loaded on the BiVO₄ photoanode with greatly improved photocurrent in comparison to that of 1.2mA·cm^-2 for BiVO₄,which is related to the fact that the hydroxide of Ni acting as a hole strengthening layer in NiFe LDH cocatalyst promotes the effective transport of photo-generated holes,thereby greatly improving the oxygen generating activity of the photo anode.It has also been reported that Ni in the NiFe LDH cocatalyst with a high Ni content will exhibit stronger and effective photogenerated carrier transfer in ionic valence change process.（2）A new type of stable and efficient cocatalyst,NiFeY LDH,was synthesized for the first time by hydrothermal method and grown in situ on a porous BiVO₄photoanode.The experimental results show that the trimetallic NiFeY LDH is more active than the bimetallic NiFe LDH and the most active LDH co-catalyst in semiconductors.In addition,compared to Y-doped Ni（OH）_x or Fe（OH）_x composites,the NiFeY LDH cocatalyst shows enhanced PEC activity of BiVO₄.The obtained NiFeY LDH/BiVO₄ photoanode displays a photocurrent density of 5.2 mA·cm^-2 under1.23 V _RHE and AM 1.5G(100 mW·cm^-2)irradiation.More importantly,the photoanode has excellent stability over 20 hours at 0.8 V_RHE.When Y is doped into the NiFe LDH structure,more surface defects are exposed due to its larger ionic radius,leading to the improved activity for PEC water oxidation.The previously reports confirmed that the surface defects of proper concentration will contribute to the increase of active sites and the rapid transfer of photo-generated electron-hole pairs of BiVO₄.This work proposes a new idea of rare earth element doped LDHs to achieve efficient photoelectrochemical water splitting performance.（3）NiOOH was prepared by hydrothermal method and grown on the BiVO₄photoanode in situ with optimal,PEC performance by etching at 100W for 30s using plasma etching machine.Compared with the NiOOH/BiVO₄ photoanode,the treated v-NiOOH/BiVO₄ photoanode can significantly enhance the oxygen production activity of the photoanode.Under the irradiation of AM 1.5G(100mW·cm^-2),1.23 V_RHE and 1M KBi solution,the photocurrent density of NiOOH/BiVO₄ photoanode is 2.8 mA·cm^-2,while v-NiOOH/BiVO₄ photoanode reach 4.3 mA·cm^-2 under the same conditions.The increase in photocurrent density illustrates that the defect is beneficial to overcome the recombination of photo-generated carriers at the interface.On this basis,FeOOH and Co（OH）_x are grown on the surface of the v-NiOOH/BiVO₄ photoanode by soaking method,both FeOOH/v-NiOOH/BiVO₄ and Co（OH）_x/v-NiOOH/BiVO₄ photoanode photocurrent density reach 5 mA·cm^-2 under the above test conditions.Besides,the initial potential reduced to 0.38 V_RHE;The increase in photocurrent density and the decrease in initial potential prove that FeOOH and Co（OH）_x as cocatalysts can effectively enhance the rapid separation of carriers and the conductivity of photoanode.