Hierarchical TiN‐Supported TsFDH Nanobiocatalyst for CO2 Reduction to Formate

Abstract The electrochemical reduction of CO 2 to value‐added products like formate represents a promising technology for the valorization of carbon dioxide. We propose a proof‐of‐concept bioelectrochemical system (BES) for the reduction of CO 2 to formate. For the first time, our device employs a nanostructured titanium nitride (TiN) support for the immobilization of a formate dehydrogenase (FDH) enzyme. The hierarchical TiN nanostructured support exhibits high surface area and wide pore size distribution, achieving high catalytic loading, and is characterized by higher conductivity than other oxide‐based supports employed for FDHs immobilization. We select the oxygen‐tolerant FDH from Thiobacillus sp. KNK65MA ( Ts FDH) as enzymatic catalyst, which selectively reduces CO 2 to formate. We identify an optimal TiN morphology for the enzyme immobilisation through enzymatic assay, reaching a catalyst loading of 59 μg cm −2 of specifically‐adsorbed Ts FDH and achieving a complete saturation of the anchoring sites available on the surface. We evaluate the electrochemical CO 2 reduction performance of the TiN/ Ts FDH system, achieving a remarkable HCOO − Faradaic efficiency up to 76 %, a maximum formate yield of 44.1 μmol mg −1 FDH h −1 and high stability. Our results show the technological feasibility of BES devices employing novel, nanostructured TiN‐based supports, representing an important step in the optimization of these devices.