Decoding Solvent Effects in Electrocatalytic Biomass Valorization: Levulinic Acid to γ-Valerolactone

Abstract

Electrocatalytic hydrogenation (ECH) of biomass-derived levulinic acid (LA) offers a sustainable route to prepare γ-valerolactone (GVL), a versatile green solvent and fuel additive. Yet despite its promise, most studies overlook the decisive role of the solvent environment, conflating conversion with true product yield. Here we disentangle these effects by systematically probing LA reduction over GC, Cu, Ni, and CuNi cathodes in three contrasting solvents (MeOH, DMSO, IPA) at two temperatures (15 and 35 °C). A clear design rule emerges: the solvents dictate the conversion ceiling, while temperature gates selectivity. At 15 °C, LA consumption is observed but productive lactonization toward GVL remains “off”, yielding only traces of HVA. At 35 °C, lactonization is unlocked, enabling GVL selectivity’s >90% in MeOH with metal-earth-abundant, Ni-based catalysts. Solvent characterization (viscosity, dielectric constant, ionic conductivity) combined with DFT analysis provides a direct rationale for the experimental trends. Methanol emerges as the most effective medium, consistent with its low viscosity and high electrolyte conductivity, which together mitigate diffusion and <em>iR</em> penalties relative to IPA and DMSO. DMSO shows intermediate performance, consistent with strong solvation/dielectric stabilization of intermediates, whereas IPA combines high viscosity and low ionic mobility, leading to the lowest conversions. Overall, efficient LA-to-GVL ECH is not dictated by conversion alone but by the coupled interplay of solvent properties, catalyst identity, and temperature required to link surface hydrogenation with thermally assisted lactonization.