Insight into electrocatalytic stability of low loading Pt-Bi/GC and Pt/GC clusters in formic acid oxidation

Abstract

Formic acid oxidation was examined on platinum-bismuth deposits on glassy carbon substrate prepared by two-step process, i.e., electrochemical deposition of Bi followed by electrochemical deposition of Pt as described in our previous article (J Electrochem Soc 161:H547-H554, 2014). Upon treatment of as-prepared clusters by slow anodic sweep, bimetallic structure consisting of Bi core occluded by Pt and Bi-oxide was obtained and exhibited significant activity and exceptional stability in HCOOH oxidation. In order to explain such electrocatalytic stability, in this work, the electrochemical properties of Pt"Bi/GC catalyst were investigated applying same protocols in supporting electrolyte with or without HCOOH and compared with Pt/GC. The protocols comprised potentiodynamic, quasi-steady-state, and chronoamperometric measurements combined with the surface characterization by COads stripping voltammetry. Application of potential cycling at Pt"Bi/GC electrode in supporting electrolyte containing HCOOH leads to minor change in surface morphology, mildly leaching of Bi from the electrode surface, and negligible decrease in activity. On the other hand, significant Bi dissolution and considerable decrease in activity are the effects of the same treatment without HCOOH. Contrary to Pt"Bi/GC, Pt/GC electrodes subjected to the same protocols exhibit completely opposite properties being more stabile during potential cycling without HCOOH than in the presence of this acid. Exceptional stability in formic acid oxidation of Pt"Bi/GC catalyst is thus most probably the result of the combination of predominant dehydrogenation path of the reaction, suppressed Bi leaching, and compensation of dissolved Bi from the core as its source due to which surface morphology endured minor changes.