High-Photovoltage Silicon Nanowire for Biological Cofactor Production

Abstract

Photocathodic conversion of NAD + to NADH cofactor is a promising platform for activating redox biological catalysts and enzymatic synthesis using renewable solar energy. However, many photocathodes suffer from low photovoltage, consequently requiring a high cathodic bias for NADH production. Here, we report an n + p-type silicon nanowire (n + p-SiNW) photocathode having a photovoltage of 435 mV to drive energy-efficient NADH production. The enhanced band bending at the n + / p interface accounts for the high photovoltage, which conduces to a benchmark onset potential [0.393 V vs the reversible hydrogen electrode (V RHE )] for SiNW-based photocathodic NADH generation. In addition, the n + p-SiNW nanomaterial exhibits a Faradaic efficiency of 84.7% and a conversion rate of 1.63 μmol h −1 cm −1 at 0.2 V RHE , which is the lowest cathodic potential to achieve the maximum productivity among SiNW-sensitized cofactor production.

Synergy Between Metal and Molecular Catalysts for (Photo)electrocatalytic 1,4-NADH Regeneration

“…(c) Concentration of 1,4-NADH as a function of time, (d) rate, faradaic efficiency, and (e) selectivity of PEC 1,4-NADH production at different potentials. (f) Comparison of 1,4-NADH production in this work and various PEC systems reported. ,, …”

“…Compared with previous reports, Figure f shows that this is among the highest performance for PEC NAD + reduction with a photocathode (details in Table S2). ,,, This PEC system shows high stability because the photocurrent density shows a negligible decline during 1 h of electrolysis (Figure S20). The high performance of PEC 1,4-NADH production is mainly contributed by the high photoresponse of the photocathode and the synergy between Cu and M, which provides a high driving force and ensures the efficient formation of M-H active species for selective 1,4-NADH production.…”

“…For the PEC NAD + reduction reaction, Si, ,, Pt/GaAs and BiFeO 3 photocathodes have been used, but they showed extremely low activities due to the low photoresponse of these photocathodes and the poor charge transfer beween the photoelectrodes and the M complex . Previously, we developed a series of polymer-based bulk heterojunction (BHJ) photocathodes for PEC water splitting, which have the advantages of high photovoltage and current density .…”

“…Various approaches, including heterogeneous, − homogeneous, − photocatalytic, − electrocatalytic, , and PEC, , avenues have been studied for NAD + reduction. (Photo)­electrocatalytic NAD + reduction with water as electron and proton donors is the most attractive.…”

Bioinspired photoelectrochemical NADH regeneration based on a molecular catalyst-modified photocathode

“…Such Si- and polythiophene semiconductor-based photocathodes could drive a dissolved molecular catalyst [Rh(Cp*)(bpy)Cl] + to selectively regenerate NADH. 15–18 The Fe 2 O 3 photoanode/BiFeO 3 photocathode tandem PEC cell was also able to drive the [Rh(Cp*)(bpy)Cl] + catalyst for NADH regeneration, which could be further used for the multienzyme cascade reaction for CO 2 reduction to methanol in a high yield. 9 Obviously, as the catalyst was mixed with the light-generated NADH in the electrolyte for such systems, there are product separation difficulties and problems of potential undesirable interaction between the [Rh(Cp*)(bpy)Cl] + catalyst and oxidoreductases.…”