In the past 20 years, enzymatic conversions have been intensely examined as a practical and environmentally friendly alternative to traditional organocatalytic conversions for chemicals and pharmaceutical intermediate production. Out of all commercial enzymes, more than one-fourth are oxidoreductases that operate in tandem with coenzymes, typically nicotinamide adenine dinucleotide (NADH) or nicotinamide adenine dinucleotide phosphate (NADPH). Enzymes utilize coenzymes as a source for electrons, protons, or holes. Unfortunately, coenzymes can be exorbitant; thus, recycling coenzymes is paramount to establishing a sustainable and affordable cell-free enzymatic catalyst system. Herein, cost-effective transition metal dichalcogenides (TMDCs), 2H-MoS2, 2H-WS2, and 2H-WSe2, were employed for the first time for direct electrochemical reduction of NAD+ to the active form of the NADH (1,4-NADH). Of the three TMDCs, 2H-WSe2 shows optimal activity, producing 1,4 NADH at a rate of 6.5 μmol cm-2 h-1 and a faradaic efficiency of 45% at -0.8 V vs Ag/AgCl. Interestingly, a self-induced surface reorganization process was identified, where the native surface oxide grown in the air was spontaneously removed in the electrochemical process, resulting in the activation of TMDCs.
Keywords: catalyst activation; electrochemical coenzyme generation; surface reorganization; transition metal dichalcogenides.