Direct electrochemical regeneration of enzymatic cofactor 1,4-NADH on a cathode composed of multi-walled carbon nanotubes decorated with nickel nanoparticles

Multi-walled carbon nanotubes (MWCNTs) were grown on a stainless steel mesh and decorated with nickel nanoparticles (Ni NPs). The developed Ni NP-MWCNT material was then used as a cathode in an electrochemical batch reactor to electrocatalytically convert NAD(+) to enzymatically-active 1,4-NADH. The regeneration of 1,4-NADH was studied at various electrode potentials. At electrode potential of -1.6V, a very high recovery (relative amount of 1,4-NADH in the product mixture) was obtained, 98 +/- 1%. In comparison, to achieve the same recovery on a non-decorated MWCNT cathode, a much higher cathodic potential was needed (-2.3V), establishing the importance of Ni NPs on the electrocatalytic activity in reducing NAD(+) to 1,4-NADH. It was postulated that hydrogen adsorbs on Ni NPs immobilized on MWCNTs to form Ni-H-ads, and this activated hydrogen rapidly reacts with neighbouring NAD-radicals, preventing the dimerization of the latter species, ultimately yielding 1,4-NADH.