Electrochemical Screening of Au/Pt Catalysts for the Thermocatalytic Synthesis of Hydrogen Peroxide Based on Their Oxygen Reduction and Hydrogen Oxidation Activities Probed via Voltammetric Scanning Electrochemical Microscopy

Electrochemical analysis provides a convenient way to screen active materials for thermocatalytic processes involving implicit electrochemical redox mechanisms. Here, we show how a combinatorial method based on scanning electrochemical microscopy (SECM) rapidly screens multiple catalysts for hydrogen peroxide direct synthesis reaction by independently analyzing their hydrogen oxidation and oxygen reduction reactivities on the same chip. We present a reproducible and quantifiable procedure to fabricate catalyst spot array samples using photolithography and microdispensing. This procedure enables the exploration of up to 10 catalysts with three replicates each on one chip, allowing us to study 30 compositions to identify reactive trends in a vast compositional space. SECM imaging with linear sweep voltammetry improved the accuracy and efficiency of data collection. Kinetic parameters of both half-reactions for each catalyst were extracted from experimental data with the help of established analytical theory and finite element analysis simulation. A library of Au_xPt_ycatalysts with a range of Au/Pt ratios from 1200:1 to 120:12 were examined. For the synthesized Au_xPt_ycatalysts, the rate constants of oxygen reduction and hydrogen reduction increase as Pt content increases and then level off beyond Au₁₂₀Pt₇. Therefore, to achieve the highest activity while keeping the cost low, Au₁₂₀Pt₇would be a promising composition to further investigate. We believe this SECM-based technique will expedite the catalyst design and discovery process for classes of thermochemical reactions involving underlying heterolytic electrochemical mechanisms, thus assisting in the synthesis and utilization of sustainable fuels and commodity chemicals.