Impurity‐Induced Electrocatalysis: Unpredicted Enhancement Effect of Ammonia Impurity Towards Formic Acid Electro‐Oxidation

Abstract

This study addresses a noteworthy unexpected enhancement of the direct oxidation pathway of formic acid (FA) to CO 2 at Pt nanoparticle-modified GC (nano-Pt/GC) electrode in the presence of ppm amounts of ammonia associated with suppressing the poisoning dehydration pathway of FA to CO, for the first time. This is reflected by a significant increase of the current intensity of the direct oxidation peak (I p d ) simultaneously with a significant decrease of the indirect oxidation peak current (I p ind ) in the presence of a minute amount of ammonia compared to that observed in its absence. For instance, the ratio I p d /I p ind increases from 0.2 in the absence of ammonia to 9.5 in the presence of 30 ppm of ammonia (i. e., 45 times higher) indicating that the direct pathway became the dominant oxidation pathway in the presence of ammonia. Ammonia is believed to favor the direct formic acid oxidation (FAO) to CO 2 as it impedes the formation of CO by disturbing the geometry of Pt sites, which is necessary for CO adsorption as evident from CO stripping experiment (i. e., prevents non-Faradic dissociation of FA). Additionally, it might induce the CH-down adsorption orientation of FA thus favoring FAO directly to CO 2 as evident from DFT calculations.