Roles of heteroatoms in electrocatalysts for alkaline water splitting:A review focusing on the reaction mechanism

Alkaline water splitting is a promising technology for“green hydrogen”generation.To improve its efficiency,highly robust catalysts are required to reduce the overpotential for low electrical power consumption.Heteroatom modification is one of the most effective strategies for boosting catalytic performance,as it can regulate the physicochemical properties of host catalysts to improve their intrinsic activity.Herein,aiming to provide an overview of the impact of heteroatoms on catalytic activity at the atomic level,we present a review of the key role of heteroatoms in enhancing reaction kinetics based on the reaction pathways of the hydrogen evolution reaction(HER)and oxygen evolution reaction(OER)in alkaline media.In particular,the introduction of heteroatoms can directly and indirectly optimize the interactions between the active sites and intermediates,thus improving the intrinsic activity.To clearly illustrate this influence in detail,we have summarized a series of representative heteroatom-modified electrocatalysts and discussed the important roles of heteroatoms in the OER and HER reaction pathways.Finally,some challenges and perspectives for heteroatom-modified electrodes are discussed.We hope that this review will be helpful for the development of efficient and low-cost electrocatalysts for water electrolysis and other energy conversion applications.

Surface modification by ligand growth strategy for dense copper bismuth film as photocathode to enhance hydrogen production activity

Hydrogen production from photoelectrochemical(PEC)water splitting has been regarded as a promising way to utilize renewable and endless solar energy.However,semiconductor film grown on photoelectrode suffers from numerous challenges,leading to the poor PEC performance.Herein,a straightforward sol-gel method with the ligand-induced growth strategy was employed to obtain dense and homogeneous copper bismuthate photocathodes for PEC hydrogen evolution reaction.By various characterizations,it was found that the nucleation and surface growth of CuBi_(2)O_(4)layer induced by 2-methoxyethanol ligand(2-CuBi_(2)O_(4))demonstrated a decent crystallinity and coverage,as well as a large grain size and a low oxygen vacancy concentration,leading to the good ability of light absorption and carrier migration.Consequently,under simulated sunlight irradiation(AM1.5G,100 mW/cm^(2)),the 2-CuBi_(2)O_(4)photocathode achieved an enhanced photocurrent density of−1.34 mA·cm^(−2)at 0.4 V versus the reversible hydrogen electrode and a promising applied bias photon-to-current efficiency of 0.586%.This surface modification by ligand growth strategy will shed light on the future design of advanced photoelectrodes for PEC water splitting.

Fermi-level-tuned MOF-derived N-ZnO@NC for photocatalysis:A key role of pyridine-N-Zn bond

For photocatalytic materials,the composites formed by metal oxides and heteroatom-doped carbon have outstanding activity.Among them,metal-organic framework(MOF)derived composites,usually composed of metal oxide and nitrogen-doped carbon,is not only simple to prepare,but also have far-exceeding catalytic performance than homogenous semiconductor.However,the relationship between the structure and performance in the photocatalytic system is still not clear.Here,we explored the tunable nitrogen configurations in sample N-ZnO@NC by controlling the thermal conversion of ZIF-8.Crucially,through exsitu and in-situ XPS characterization,it is found that the ZnO and nitrogen-doped carbon in N-ZnO@NC are connected by C-N-Zn bond,which enhances charge separation efficiency and becomes the origin of superior photocatalytic performance.DFT calculations further reveal the influence of different Zn-bonding nitrogen configurations on the adjusting of Fermi level and electron transfer.This study exhibits that the pyridine-N configuration in MOF-derived material is the main contributor for the improved performance and tunes Fermi level more appropriately than the pyrrolic-N,which can hold the key for future design of next-generation photocatalysts.