Continuous 3D Titanium Nitride Nanoshell Structure for Solar‐Driven Unbiased Biocatalytic CO₂ Reduction

Abstract

Abstract Z‐scheme‐inspired tandem photoelectrochemical (PEC) cells have received attention as a sustainable platform for solar‐driven CO 2 reduction. Here, continuously 3D‐structured, electrically conductive titanium nitride nanoshells (3D TiN) for biocatalytic CO 2 ‐to‐formate conversion in a bias‐free tandem PEC system are reported. The 3D TiN exhibits a periodically porous network with high porosity (92.1%) and conductivity (6.72 × 10 4 S m −1 ), which allows for high enzyme loading and direct electron transfer (DET) to the immobilized enzyme. It is found that the W‐containing formate dehydrogenase from Clostridium ljungdahlii (ClFDH) on the 3D TiN nanoshell is electrically activated through DET for CO 2 reduction. At a low overpotential of 40 mV, the 3D TiN‐ClFDH stably converts CO 2 to formate at a rate of 0.34 µmol h −1 cm −2 and a faradaic efficiency (FE) of 93.5%. Compared to a flat TiN‐ClFDH, the 3D TiN‐ClFDH shows a 58 times higher formate production rate (1.74 µmol h −1 cm −2 ) at 240 mV of overpotential. Lastly, a bias‐free biocatalytic tandem PEC cell that converted CO 2 to formate at an average rate of 0.78 µmol h −1 and an FE of 77.3% only using solar energy and water is successfully assembled.