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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 (VRHE)] 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 VRHE, which is the lowest cathodic potential to achieve the maximum productivity among SiNW-sensitized cofactor production.

Cations in an electrolyte modulate microenvironments near the catalyst surface and affect product distribution from an electrochemical CO 2 reduction reaction, and thus, their interaction with intermediate states has been tried to be probed. Herein, we directly observed the cation effect on *CO intermediates on the Cu(OH) 2 -derived catalyst in real time through operando surface-enhanced Raman spectroscopy at high overpotentials (-1.0 V RHE ). Atop *CO peaks are composed of low-frequency binding *CO (*CO LFB ) and high-frequency binding *CO (*CO HFB ) because of their adsorption sites. These two *CO intermediates are found to have different sensitivities to the cation-induced field, and each *CO is proposed to be suitably stabilized for efficient C-C coupling. The proportions between *CO HFB and *CO LFB are dependent on the type of alkali cations, and the increases in the *CO HFB ratio have a high correlation with selective C 2 H 4 production under K + and Cs + , indicating that *CO HFB is the dominant and fast active species. In addition, as the hydrated cation size decreases, *CO LFB is more sensitively red-shifted than *CO HFB , which promotes C-C coupling and suppresses C 1 products. Through time-resolved operando measurements, dynamic changes between the two *CO species are observed, showing the rapid initial adsorption of *CO HFB and subsequently reaching a steady ratio between *CO LFB and *CO HFB .

While atomically monodisperse nanostructured materials are highly desirable to unravel the size- and structure-catalysis relationships, their controlled synthesis and the atomic-level structure determination pose challenges. Particularly, copper-containing atomically precise alloy nanoclusters are potential catalyst candidates for the electrochemical CO 2 reduction reaction (eCO 2 RR) due to high abundance and tunable catalytic activity of copper. Herein, we report the synthesis and total structure of an alkynyl-protected 21-atom AgCu alloy nanocluster [Ag 15 Cu 6 (C≡CR) 18 (DPPE) 2 ] - , denoted as Ag 15 Cu 6 (HC≡CR: 3,5-bis(trifluoromethyl)phenylacetylene; DPPE: 1,2-bis(diphenylphosphino)ethane). The single-crystal X-ray diffraction reveals that Ag 15 Cu 6 consists of an Ag 11 Cu 4 metal core exhibiting a body-centered cubic (bcc) structure, which is capped by 2 Cu atoms, 2 Ag 2 DPPE motifs, and 18 alkynyl ligands. Interestingly, the Ag 15 Cu 6 cluster exhibits excellent catalytic activity for eCO 2 RR with a CO faradaic efficiency (FE CO ) of 91.3% at -0.81 V (vs the reversible hydrogen electrode, RHE), which is much higher than that (FE CO : 48.5% at -0.89 V vs RHE) of Ag 9 Cu 6 with bcc structure. Furthermore, Ag 15 Cu 6 shows superior stability with no significant decay in the current density and FE CO during a long-term operation of 145 h. Density functional theory calculations reveal that the de-ligated Ag 15 Cu 6 cluster can expose more space at the pair of AgCu dual metals as the efficient active sites for CO formation.