Bi-modified Pt Electrodes toward Glycerol Electrooxidation in Alkaline Solution: Effects on Activity and Selectivity

Abstract

Herein we investigate the effect of irreversibly adsorbed bismuth on polycrystalline platinum (Pt p) on the electrooxidation of glycerol in alkaline media by combining electrochemical, spectroscopic (in situ FTIR) and analytical (HPLC on line) techniques. We found that the activity of Pt p increases by about fivefold when the optimal quantity of Bi ions is added to the solution. Besides, the adatom strongly impacts the reaction products by suppressing the pathways with CC bond breaking, hindering the formation of CO (and other unknown intermediates) and enhancing the production of Glycerate. Different to the results in acid media for Pt p-Bi systems where Bi block the oxidation pathway through the primary carbon, glycerate is the main product in alkaline media and dihydroxyacetone is either produced in extremely low quantities or not produced. Besides, comparing our results with those in acid media, the peak current recorded at 1 mV.s-1 in this work was one order of magnitude higher. These results show the strong impact of the pH in the reaction rate and selectivity.

Insights on the unique electro-catalytic behavior of PtBi/C materials

“…to be much higher, according to both MDs simulations and electrochemical characterizations, which could prevent the formation of multi-bonded intermediates and favor mainly singlebonded intermediates due to a steric effect, leading mainly to glyceraldehyde at low potentials and glycerate at higher potentials. This observation was also made by De Souza et al 54 for the glycerol electrooxidation in alkaline medium on Pt electrodes modified by Bi adatoms.…”

“…On the other hand, the structure of Bi deposits on Pt surface in the present case differs from that of adatoms in the case of Garcia et al 55 and De Souza et al 54 . First, molecular dynamics simulation predicted the formation of Bi dimers and trimers.…”

“…increase of the activity without significant shift of the onset potential, was observed from ca. 0.4 V vs. RHE by de Souza et al 54…”

Glycerol Electro-Oxidation in Alkaline Media and Alkaline Direct Glycerol Fuel Cells

“…The addition of p group elements, such as bismuth and Sn, to Pt, Pd and Au catalysts results in a lower glycerol oxidation onset potential and a higher GOR activity, and gives rise to a change in selectivity. The addition of bismuth and tin to platinum leads to reduce/suppress the dissociative adsorption of glycerol (C-C bond breaking) and the formation of adsorbed CO species, enhancing the selectivity toward C3 products [59,60,72]. Bismuth hinders C-C bond cleavage both in acid and alkaline media, but while in acid medium Bi presence results in the formation of DHA with 100% selectivity [90], in alkaline media GLA is the main product, and DHA is either produced in extremely low quantities or not produced [59,60].…”

“…The addition of bismuth and tin to platinum leads to reduce/suppress the dissociative adsorption of glycerol (C-C bond breaking) and the formation of adsorbed CO species, enhancing the selectivity toward C3 products [59,60,72]. Bismuth hinders C-C bond cleavage both in acid and alkaline media, but while in acid medium Bi presence results in the formation of DHA with 100% selectivity [90], in alkaline media GLA is the main product, and DHA is either produced in extremely low quantities or not produced [59,60]. Indeed, in acid medium Bi blocks the pathway for primary oxidation and also provides a specific Pt-Bi surface site for secondary alcohol oxidation, but in alkaline medium the OH − presence suppress the blocking of the pathway for primary oxidation, giving rise to the formation of GALD and GLA.…”