Potential dependence of gluconic acid to glucose electroreduction on silver

Abstract

The electrocatalytic conversion of gluconic acid, an aldonic acid, as a model component of spent sulfite liquor (SSL) represents a green approach for side stream valorization. The biotechnological valorization of SSL to more valuable products is inhibited by aldonic acids. Here, we discovered silver as an electrocatalyst for the reduction of gluconic acid to glucose as a sustainable strategy to convert aldonic acids into fermentable carbohydrates. A potential screening in a two-electrode compartment cell was performed and showed the best conversion at −1.56 V vs. reversible hydrogen electrode (RHE) with 0.296 mmol L⁻¹. The conversion rate decreased with higher and lower potentials than −1.56 V vs. RHE. SEM, EDS, and XPS analyses revealed no clear influence of the reaction on the electrocatalyst. LEIS measurements indicated only ion adsorption from the electrolyte and a slight surface oxidation. The electrocatalytic behavior of silver reveals a similar trend to that of electrocatalytic CO₂ reduction reaction and nitrogen reduction reaction, where a maximum conversion is reached at one cathodic potential before the hydrogen reduction reaction becomes dominant. This highlights a key challenge in merging electrocatalysis and the biorefinery concept to create a bioelectrorefinery for side stream valorization, a crucial element of a bio-circular-green economy.