Adjusting oxygen vacancies in perovskite LaCoO_(3)by electrochemical activation to enhance the hydrogen evolution reaction activity in alkaline condition

Developing highly-active,earth-abundant non-precious-metal catalysts for hydrogen evolution reaction(HER)in alkaline solution would be beneficial to sustainable energy storage.Perovskite oxides are generally regarded as low-active HER catalysts,due to their inapposite hydrogen adsorption and water dissociation.Here,we report a detailed study on perovskite LaCoO_(3)epitaxial thin films as a model catalyst to significantly enhance the HER performance via an electrochemical activation process.As a result,the overpotential for the activation films to achieve a current density of 0.36 m A/cm^(2)is 238 m V,reduced by more than 200 m V in comparison with that of original samples.Structural characterization revealed the activation process dramatically increases the concentration of oxygen vacancies(Vo)on the surface of LaCoO_(3).We established the relationship between the electronic structure induced by Vo and the enhanced HER activity.Further theoretical calculations revealed that the Vo optimizes the hydrogen adsorption and dissociation of water on the surface of LaCoO_(3)thin films,thus improving the HER catalytic activity.This work may promote a deepened understanding of perovskite oxides for HER mechanism by Vo adjusting and a new avenue for designing highly active electrochemical catalysts in alkaline solution.

Transparent conductive SnO_(2)thin films via resonant Ta doping

Transparent conductive oxide(TCO)thin films are highly desired as electrodes for modern flat-panel displays and solar cells.Alternative indium-free TCO materials are highly needed,because of the scarcity and the high price of indium.Based on the mechanism of resonant doping,Ta has been identified as an effective dopant for SnO_(2)to achieve highly conductive and transparent TCO.In this work,we fabricated a series of Ta-doped SnO_(2)thin films(Sn_(1-x)Ta_(x)O_(2),x=0.001,0.01,0.02,0.03)with high conductivity and high optical transparency via a low-cost sol-gel spin coating method.The Sn_(0.98)Ta_(0.02)O_(2)film achieves the highest electrical conductivity of 855 S cm-1with a carrier concentration of2.3×10^(20)cm^(-3)and high mobility of 23 cm^(2)V^(-1)s^(-1).The films exhibit a very high optical transparency of 89.5%in the visible light region.High-resolution X-ray photoemission spectroscopy and optical spectroscopy were combined to gain insights into the electronic structure of the Sn_(1-x)Ta_(x)O_(2)films.The optical bandgaps of the films are increased from 3.96 eV for the undoped SnO_(2)to 4.24 eV for the Sn_(0.98)Ta_(0.02)O_(2)film due to the occupation of the bottom of conduction band by free electrons,i.e.,the Burstein-Moss effect.Interestingly,a bandgap shrinkage is also directly observed due to the bandgap renormalization arising from many-body interactions.The double guarantee of transparency and conductivity in Sn_(1-x)Ta_(x)O_(2)films and the low-cost growth method provide a new platform for optoelectronic and solar cell applications.