A series of experiments were conducted to investigate the source of the proton in the hydrodeoxygenation products (Figure ). The use of d7-DMF did not result in deuterium incorporation in the alkane product 2a, confirming that this solvent is a poor proton-donor. Thus, the tetrabutylammonium cation of the supporting electrolyte and/or borohydride counterion appeared as a plausible source of protons via Hofmann elimination. To probe this hypothesis, reactions were carried out using a supporting electrolyte unable of undergoing such elimination: KPF6. Indeed, the use of this salt resulted in a significantly lower yield of product 2a under otherwise identical conditions, suggesting that the tetrabutylammonium-based supporting electrolyte is not only enhancing the conductivity of the reaction medium under standard conditions but also acting as proton source. This conclusion was further supported by a reaction carried out with KPF6 in the proton-donating solvent N-methylformamide (NMF) that restored the yield to a significant extent (Figure ). Furthermore, a reaction using deuterated benzyl alcohol (d-1b) resulted in deuterium incorporation into product 2b, thus demonstrating that hydroxyl protons may too act as hydrogen source in the present system.