Solar-boosted Electrocatalytic Water Splitting Over The Electrodes Of Decorated Fe-based-metal Compounds

Electrolytic water splitting by using clean and renewable energy to produce hydrogen with high-energy-density is one of the important mean to ensure energy security and realize the sustainable development of the national economy.Water electrolysis has two half-reactions of hydrogen evolution（HER）and oxygen evolution（OER）.Both HER and OER are endothermic reactions.Its practical application is always hindered by their high reaction potentials,large energy consumption,and low conversion efficiency.Photo-assisted electrocatalytic water splitting can use solar energy to increase the driving force of the water splitting and improve the efficiency.However,the study of the photo-assisted electrocatalytic water splitting still remains in the infancy.Its bottleneck is how to couple and optimize the photoactive species and the electroactive species,to construct an efficient photo-assisted electrocatalyst and catalytic reaction system,and to maximize the synergistic effect of light energy and electric energy.In this paper,Fe-based metal compounds used as electroactive components are modified with photoactive components via decoration or in-situ growth strategies to construct three-dimensional photo-assisted electrocatalytic electrodes.Benefiting from the advantage of the contact between the photoactive component and the electroactive component,the exposure of the electroactive site and the three-dimensional structure,the ohmic polarization and diffusion polarization in the process of water splitting can be weakened effectively,and the mass transfer and load transfer capacity can be improved,thus enhancing the activity and stability of photo-assisted electrocatalytic water splitting.The promoting effect of light energy on the electrocatalytic water splitting reaction have been confirmed by the experiments with or without light irradiation.The main research contents are as follows:（1）Cu₂O-modified CoP_x nanowire arrays are used in photo-assisted electrocatalytic HER reaction.In this part of work,Cu₂O nanoparticles were modified on the surface of CoP_x nanowires by liquid deposition method to obtain a self-supporting Cu₂O-CoP_xelectrode.With AM 1.5 irradiation,the Cu₂O-CoP_x achieved an overpotential of 58 m V at 100 m A cm^-2 in 1.0 M KOH,which was lower than that without light(88 m V at 10 m A cm^-2).Under AM 1.5 irradiation,the photo-generated electrons generated from Cu₂O are injected into CoP_x,which promotes the upward shift of the Fermi level of CoP_x,increasing the driving force of the catalytic reaction,and thereby reducing the overpotential of HER.At the same time,the photo-generated holes are transferred to the counter electrode under the external electric field.This study confirms the possibility of photo-assisted electrocatalysis HER,and opens up a new way for the use of solar energy to design more energy-efficient and environmentally friendly catalytic water splitting systems.（2）CeO_x-modified FeOOH/FeNi₃ arrays are used for photo-assisted electrocatalytic OER reaction.In this part of work,CeO_x-dotted Fe OOH/FeNi₃ self-supporting electrodes were constructed on the surface of carbon cloth through the continuous hydrothermal and electrodeposition reactions.Under AM 1.5 irradiation,the overpotential of the CeO_x-F@FeNi₃-CC electrode is reduced by 16 m V to reach 100 m A cm^-2.Under AM 1.5irradiation,the photo-generated holes generated from CeO_x are transferred to Fe OOH/FeNi₃,which increases the OER activity of the electrocatalyst.At the same time,the photo-generated electrons are transferred to the counter electrode.It follows that embellish strategy can not only ensure effective contact between the photoactive and electroactive components with matching energy levels,but also fully expose the electroactive sites.This study proves the advantage of photo-assisted electrocatalytic water splitting,and also provides a way to design materials.（3）CoCrLDH 3D structure electrode is designed for photo-assisted electrocatalysis of OER.In this part of work,Co Cr LDH nanosheet arrays was constructed on the surface of carbon paper by the hydrothermal method.Under AM 1.5 irradiation,the optimal Co Cr LDH shows a more than 1.5-fold enhanced OER intrinsic activity and a 1.8-fold increase in H₂ evolution achieving.The photogenerated holes generated from the photoactive Cr species oxidize the surrounding Co species,increasing the number of highly active Co³⁺in the catalyst,and enhancing the intrinsic activity of the material to catalyze OER.At the same time,the photogenerated electrons are transferred to the cathode to promote HER under the driving force of an external electric field.In addition,in Co Cr LDH,the photoactive component and the electroactive component are connected by chemical bonds,which effectively reduce the interface resistance and accelerate the charge transfer.This study fully proves that the motivation of light for the electrocatalytic reaction is improved remarkablely after eliminating the ohmic polarization of the interface,which provides a new strategy for the preparation of photo-assisted electrocatalytic water splitting materials.