Wired: With silicon as a photocathode and [Ni(bpy)2] as a catalyst, visible light‐powered CO2 photofixation is made possible (see picture). Owing to their multifaceted surfaces, silicon nanowires show a significantly better performance compared to planar Si. The shape of a nanowire is indeed an appealing materials choice for high‐efficiency, low‐cost solar energy conversion applications.

Wired: With silicon as a photocathode and [Ni(bpy)2] as a catalyst, visible light‐powered CO2 photofixation is made possible (see picture). Owing to their multifaceted surfaces, silicon nanowires show a significantly better performance compared to planar Si. The shape of a nanowire is indeed an appealing materials choice for high‐efficiency, low‐cost solar energy conversion applications.

(Liu R)) plex polymer junction by Chardon-Noblat et al. [16]. The Faradic efficiency was measured at 63% in aqueous solutions. These results are encouraging because they show that catalysts can not only increase the efficiency when converting solar energy into chemical energy, but also increase the product selectivity by limiting the reaction pathway, especially for CO 2 photoreduction. Concurrently, our group has demonstrated that high product selectivity can be achieved by avoiding directly passing electrons to carbon in CO 2 [17,18]. Instead, when a reactive intermediate is activated by light-driven reactions, it binds with and reduces CO 2 in a highly specific manner. Our approach is inspired by dark reactions in natural photosynthesis. We have shown that the reactive intermediate can be a substrate or a metal catalyst (Scheme 1), the latter of which promises a broader scope of reactions. Building upon our previous success, herein we report that the redox potentials of the intermediate can be readily tuned to match the reducing power of the Si nanowire photocathode.Controlling redox potentials of catalysts is important because how they align with the energetics of the photoelectrode determines the ease or difficulty of charge transfer at the electrode/catalyst interface. For instance, for reduction reactions, the redox potential of the catalyst needs to be more negative than the Fermi level of the semiconductor to allow for the flow of electrons from semiconductor to catalyst. Additionally, the overpotential of the charge transfer from semiconductor to catalyst should be sufficiently small. All these considerations add extra challenges to find suitable semiconductor/catalyst pairs for practical CO 2 reduction. The semiconductors are limited by the following requirement in a high efficient photoelectrochemical cells: 1) suitable band gap to absorb large portion of solar light; 2) high-quantum efficiency of light to electron conversion; 3) long charge diffusion length of the bulk material to reduce charge recombination; 4) earth abundance for low cost at large scales. Only a handful of semiconductors meet these