Environmental TEM Study of Electron Beam Induced Electrochemistry of Pr0.64Ca0.36MnO3 Catalysts for Oxygen Evolution

Abstract

Environmental transmission electron microscopy (ETEM) studies offer great potential for gathering atomic scale information on the electronic state of electrodes in contact with reactants. It also poses big challenges due to the impact of the high energy electron beam. In this article, we present an ETEM study of a Pr0.64Ca0.36MnO3 (PCMO) thin film electrocatalyst for water splitting and oxygen evolution in contact with water vapor. We show by means of off-axis electron holography and electrostatic modeling that the electron beam gives rise to a positive electric sample potential due to secondary electron emission. The value of the electric potential depends on the primary electron flux, the sample’s electric conductivity and grounding, and gas properties. We present evidence that two observed electrochemical reactions are driven by a beam induced electrostatic potential of the order of a volt. The first reaction is an anodic oxidation of oxygen depleted amorphous PCMO which results in recrystallization of the oxide. The second reaction is oxygen evolution which can be detected by the oxidation of a silane additive and formation of SiO2–y at catalytically active surfaces. The quantification of beam induced potentials is an important step for future controlled electrochemical experiments in an ETEM.