Carbon Nanohorn Support for Solar driven CO₂ Reduction to CO Catalyzed by Mn‐complex in an All Earth‐abundant System

Abstract An Mn‐complex supported on multi‐walled carbon nanotubes (MWCNTs) has been reported to be a superior catalyst for CO₂ reduction to CO, where the carbon support strongly influences the catalytic activity, enabling operation at a low overpotential. Here, the effects of various carbon supports on the activity of a Mn‐complex catalyst were investigated. Among the various carbon supports, which included carbon black and MWCNTs, carbon nanohorns (CNHs) were the best support for enhancing the catalytic activity of the Mn‐complex toward CO₂ reduction. This enhancement was attributed to the CNHs’ high specific surface area and hydrophobic nature. For solar‐driven CO₂ reduction to CO, the Mn‐complex catalyst supported on CNHs was series‐connected to Ni‐doped β‐FeOOH as a water oxidation catalyst via a Si solar cell; a solar‐to‐CO conversion efficiency of 3.3±0.4% was achieved in a single‐compartment reactor.