Electrolyte selection toward efficient photoelectrochemical glycerol oxidation on BiVO₄

Glycerol, a primary by-product of biodiesel production, can be oxidized into various value-added chemicals, significantly enhancing the techno-economic value of photoelectrochemical (PEC) cells. Several studies have explored various photoelectrode materials and co-catalysts, but the influence of electrolytes on PEC glycerol oxidation has remained relatively unexplored despite its significance. Here, we explore the impact of various acidic (pH = 2) electrolytes, namely NaNO₃, NaClO₄, Na₂SO₄, K₂SO₄, and KP_i, on PEC glycerol oxidation using nanoporous thin film BiVO₄ as a model photoanode. Our experimental findings reveal that the choice of electrolyte anion and cation significantly affects the PEC performance (i.e., photocurrent, onset potential, stability, and selectivity towards value-added products) of BiVO₄ for glycerol oxidation. To explain this interesting phenomenon, we correlate the observed performance trend with the ion specificity in the Hofmeister series as well as the buffering capacity of the electrolytes. Notably, NaNO₃ is identified as the optimal electrolyte for PEC glycerol oxidation with BiVO₄ when considering various factors such as stability and production rates for glycerol oxidation reaction (GOR) products, surpassing the previously favored Na₂SO₄. Glycolaldehyde emerges as the most dominant product with ∼50% selectivity in NaNO₃. The general applicability of our findings is confirmed by similar observation in electrochemical (EC) GOR with a polycrystalline platinum anode. Overall, these results emphasize the critical role of electrolyte selection in enhancing the efficiency of EC/PEC glycerol oxidation.