Direct electrocatalytic reduction of coenzyme NAD+ to enzymatically-active 1,4-NADH employing an iridium/ruthenium-oxide electrode

•Ir0.8Ru0.2-oxide coating was formed thermally on a Ti substrate.•Electrochemical regeneration of enzymatically-active 1,4-NADH was investigated.•The 1,4-NADH recovery percentage is strongly dependent on the electrode potential.•A highest recovery, 88%, was obtained at −1.70 V vs. MSE.•The NADH regeneration process involved electrochemical hydrogenation.

A thermally prepared iridium/ruthenium-oxide coating (Ir0.8Ru0.2-oxide) formed on a titanium substrate was investigated as a possible electrode for direct electrochemical regeneration of enzymatically-active 1,4-NADH from its oxidized form NAD+, at various electrode potentials, in a batch electrochemical reactor. The coating surface was characterized by ‘cracked mud’ morphology, yielding a high surface roughness. The NADH regeneration results showed that the percentage of enzymatically-active 1,4-NADH present in the product mixture (i.e. recovery) is strongly dependent on the electrode potential, reaching a maximum (88%) at −1.70 V vs. MSE. The relatively high recovery was explained on the basis of availability of adsorbed ‘active’ hydrogen (Hads) on the Ir/Ru-oxide surface, i.e. on the basis of electrochemical hydrogenation.