Formic Acid Oxidation at Platinum-Bismuth Clusters

Abstract

Formic acid oxidation was studied on platinum-bismuth deposits on glassy carbon (GC) substrate. The catalysts of equimolar ratio were prepared by potentiostatic deposition using chronocoulometry. Bimetallic structures obtained by two-step process, comprising deposition of Bi followed by deposition of Pt, were characterized by AFM spectroscopy which indicated that Pt crystallizes preferentially onto previously formed Bi particles. The issue of Bi leaching (dissolution) from PtBi catalysts, and their catalytic effect alongside the HCOOH oxidation is rather unresolved. In order to control Bi dissolution, deposits were subjected to electrochemical oxidation, in the relevant potential range and supporting electrolyte, prior to use as catalysts for HCOOH oxidation. Anodic striping charges indicated that along oxidation procedure most of deposited Bi was oxidized. ICP mass spectroscopy analysis of the electrolyte after this electrochemical treatment revealed that Bi was only partly dissolved indicating the possibility for formation of some Bi oxide species. Moreover, EDX analysis of the as prepared (Pt@Bi/GC) catalysts and those oxidized confirmed appreciably higher content of oxygen in the latter. Catalysts prepared in this way exhibit about 10 times higher activity for formic acid oxidation in comparison to pure Pt, as revealed both by potentiodynamic and quasy-potentiostatic measurements. This high activity is the result of well-balanced ensemble effect induced by Bi-oxide species interrupting Pt domains. Prolonged cycling and chronoamperometry tests disclosed exceptional stability of the catalyst during formic acid oxidation. The activity is compatible with the activity of previously studied Pt 2 Bi alloy but the stability is significantly better.

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

“…Equimolar platinum-coated bismuth deposits on glassy carbon substrate were prepared by a two-step process using chronocoulometry at −0.1 V [11]. Shortly, the controlled amount of Bi was electrodeposited onto glassy carbon (GC) substrate from 2 mM Bi perchlorate in 0.1 M H 2 SO 4 and subsequently coated with a thin Pt layer from 1 mM H 2 PtCl 6 solution.…”

“…For the molar ratio Pt:Bi = 1:1, the deposited charge corresponds to 11.02 μg cm −2 for Bi and 10.3 μg cm −2 for Pt. Microscopic (AFM and STM) analysis of as-prepared catalyst combined with cyclic voltammetry revealed that Pt crystallized preferentially onto previously formed Bi particles, and approximately spherical Bi-Pt clusters were formed but that Bi was not completely occluded by Pt [11]. In order to control Bi dissolution, upon deposition of both components, electrochemical oxidation of Bi was carried out using linear-sweep voltammetry (ν=1 mV s −1 ) in the range from −0.27 to 0.8 V. Two successive sweeps were recorded to confirm the entirety of the Bi oxidation.…”

“…In effort to overcome these problems, many Pt-based binary alloys have been investigated in terms of their oxidation onset potential as well as current density and their tolerance to CO [4][5][6][7][8][9]. In general, these bimetallic catalysts exhibit improved properties regarding electrocatalytic activity for the oxidation of formic acid and poisoning by CO but their stability depend on the leaching of less noble metal [10][11][12][13][14]. Among the studied catalysts, PtBi intermetallics as well Pt 2 Bi alloy exhibited superior electrocatalytic activity toward the oxidation of formic acid and high tolerance against CO [15][16][17][18][19][20][21].…”

“…In our previous work [11], formic acid oxidation was studied on platinum-bismuth deposits on glassy carbon substrate obtained by two-step process, comprising deposition of Bi followed by deposition of Pt. AFM, STM, and EDX characterization of the catalysts obtained indicated equimolar ratio of the deposit components as well as that Pt crystallized preferentially onto previously formed Bi particles resulting in the formation of approximately spherical clusters of Bi covered by Pt.…”

“…In this work, which represents a continuation research of the electrochemical properties of low loading Pt@Bi/GC catalyst prepared according to the procedure described in our previous article [11], the reaction of formic acid oxidation was studied using potentiodynamic, quasi-steady-state, and chronoamperometric measurements. The main objective was to consider the stability of Pt@Bi/GC catalyst with respect to this reaction.…”