High-Throughput Screening of Hydrogen Peroxide (Electro)Catalysts Using Scanning Electrochemical Microscopy (SECM)

Abstract

Hydrogen peroxide (H 2 O 2 ) is a powerful, versatile and environmentally benign oxidant that has gained relevance in industrial settings. Direct synthesis of H 2 O 2 from O 2 and H 2 , which is a method with low pollution and on-site production at potentially low cost, has attracted great interest. To realize this synthetic process, catalysts of high efficiency need to be developed to facilitate the reaction. In this study, scanning electrochemical microscopy (SECM) methods were used to conduct high-throughput screening of bimetallic nanoparticle catalysts (consisting of Au, Pt, Ni, etc.) for H 2 O 2 generation from direct synthesis. In order to achieve high-throughput analysis, samples with multiple catalysts were fabricated. We used photolithography to produce wells that confined catalyst spots of a library of materials. Gold nanoparticles (AuNPs) were dispensed into these wells with a microdispenser, leaving the same amount of AuNPs at each spot. Droplets of corresponding metal salt solutions were added into the wells and then annealed to form bimetallic catalyst spots. The morphology and composition of fabricated spot arrays were characterized with SEM, TEM and EDS. SECM measurements were performed to study the catalytic reactivity of the catalyst spots for H 2 O 2 direct synthesis. From an electrochemical point of view, the entire process of H 2 O 2 direct synthesis from H 2 and O 2 can be split into two half reactions, oxygen reduction and hydrogen oxidation. The first half reaction, oxygen reduction reaction (ORR), is a two-electron process reducing O 2 into H 2 O 2 . The second half reaction, hydrogen oxidation reaction (HOR), converts H 2 to protons. Only when a catalyst exhibits outstanding catalytic reactivity towards both two reactions, does it catalyze H 2 O 2 direct synthesis efficiently in a thermocatalytic system. The catalytic reactivity for the two half reactions was investigated separately in a high throughput manner by SECM as the technique acquired information from the entire spot array in one scan and revealed catalytic performance for each spot in the array. SECM images were obtained to visualize catalytic reactivity of the spot array. Finite element analysis simulation was done in COMSOL Multiphysics to acquire theoretical values for SECM experiments. The ultimate goal of this study is to identify a catalyst of a specific composition with the best catalytic reactivity for overall H 2 O 2 direct synthesis. Such catalyst can be used in industrial H 2 O 2 production to improve production efficiency and to reduce cost.