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

Abstract

Z-scheme in natural photosynthesis are promising for solar-driven CO 2 conversion. [2] By combining multiple photoelectrodes or photovoltaics (PV), the Z-scheme PEC cells can provide sufficient photopotential to simultaneously drive water oxidation and CO 2 reduction under minimal or no external bias. [3] Nevertheless, lowering the kinetic barrier of thermodynamically inert CO 2 remains a hurdle for efficient CO 2 reduction. The development of CO 2reducing biocatalyst-conjugated cathodes can improve chemoselectivity and increase yield under mild conditions. [4] Compared to synthetic catalysts that often require extreme conditions such as high pressure, pH, or temperature, enzymes show high catalytic activities and specificities under mild conditions, making them a valuable catalyst for sustainable and green applications. In particular, formate dehydrogenase (FDH) is an attractive redox enzyme that reduces CO 2 to formate, an alternative water-soluble feedstock that can be easily converted to other common fuels. [5] Previous studies have focused on mediated electron transfer (MET)-type reactions, [6] in which redox mediators such as nicotinamide adenine dinucleotide cofactor (NADH) and Rh-based complexes shuttle electrons between an electrode and FDH. However, the MET-based biocatalysis requires costly electron mediators and multiple electron transfer steps that cause side reactions and significant losses in efficiency. [7] Here, we report the development of 3D titanium nitride nanoshell (3D TiN) electrodes for biocatalytic PEC cells that convert CO 2 to formate through direct electron transfer (DET), as depicted in Scheme 1a. A highly ordered, porous TiN structure is employed as an electrically conductive scaffold for efficient DET to a W-containing FDH from Clostridium ljungdahlii (ClFDH) (inset, Scheme 1a). TiN was chosen as a scaffold for DET-based bioelectrode because it is highly conductive, electrochemically stable and exhibit high chemical and thermal resistance, as well as exceptional hardness. [8] The 3D TiN electrode simultaneously provides (i) a large electroactive surface area generated from an ultrathin (≈30 nm), 3D nanoshell structure with high porosity (92.1%) for high enzyme loading per geometric area, (ii) a continuous electron transfer network with high electrical 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...

CO2‐Reductive, Copper Oxide‐Based Photobiocathode for Z‐Scheme Semi‐Artificial Leaf Structure

“…These features have elicited extensive research on the combination of dual photoelectrodes in the Z‐scheme configuration for solar‐to‐fuel conversion . However, the realization of artificial photosynthesis remains challenging, owing to intrinsic limitations of photoelectrode materials and the kinetic and thermodynamic barriers of CO 2 activation in mild conditions . For example, some cutting‐edge PEC systems require an external bias to satisfy the thermodynamic driving force of CO 2 reduction under light irradiation.…”

“…Herein we report a copper oxide‐based, Z‐scheme semi‐artificial leaf structure that employs an enzyme–semiconductor photobiocathode for CO 2 ‐to‐formate conversion by directly transferring photoexcited electrons to FDH (Scheme ). The FDH from Clostridium ljungdahlii (ClFDH) is a highly efficient CO 2 ‐to‐formate‐converting electrocatalyst that contains electron‐transfer relays via a FeS cluster and a W active center . We chose a CuFeO 2 and CuO‐mixed p‐type photocathode (CuFeO 2 |CuO, CFO) because of its negative conduction band edge potential to reduce the active site of ClFDH under visible light.…”

On the Crystal Chemistry of Inorganic Nitrides: Crystal-Chemical Parameters and Opportunities in the Exploration of Their Compositional Space

“…Large-scale computational 3,21 and synthetic efforts (notably by the groups of Francis DiSalvo, Rainer Niewa, Wolfgang Schnick, and Duncan Gregory) to explore their compositional space are underway. These compounds are being investigated for energy conversion and storage, 22 solar-driven CO2 reduction in Z-scheme-inspired photoelectrochemical cells, 23 as alternatives to metals, metal oxides and metal sulfides in heterogeneous catalysis, 24 in quantum information processing, 25 as piezoelectric 26,27 and photoluminescent 28 materials, electrocatalysts, 29,30 electrochemical sensors, 31 photocatalysts, 32,33 photovoltaics, [34][35][36] photodetectors, 37,38 light-emitting diodes, 39,40 thermoelectrics, 26,41 superconductors, [42][43][44] as hard coating 45 and ultrahard materials 46 (in their pernitride form), etc. With a relatively slow start compared to oxides and oxysalts, it is no surprise that some of the most exciting properties of these materials are currently being realized, and that much promise lies ahead in the exploratory synthesis of functional inorganic nitrides.…”

On the Crystal Chemistry of Inorganic Nitrides: Crystal-Chemical Parameters, Bonding Behavior, and Opportunities in the Exploration of Their Compositional Space

“…Large-scale computational 3,21 and synthetic efforts (notably by the groups of Francis DiSalvo, Rainer Niewa, Wolfgang Schnick, and Duncan Gregory) to explore their compositional space are underway. These compounds are being investigated for energy conversion and storage, 22 solar-driven CO2 reduction in Z-scheme-inspired photoelectrochemical cells, 23 as alternatives to metals, metal oxides and metal sulfides in heterogeneous catalysis, 24 in quantum information processing, 25 as piezoelectric 26,27 and photoluminescent 28 materials, electrocatalysts, 29,30 electrochemical sensors, 31 photocatalysts, 32,33 photovoltaics, [34][35][36] photodetectors, 37,38 light-emitting diodes, 39,40 thermoelectrics, 26,41 superconductors, [42][43][44] as hard coating 45 and ultrahard materials 46 (in their pernitride form), etc. With a relatively slow start compared to oxides and oxysalts, it is no surprise that some of the most exciting properties of these materials are currently being realized, and that much promise lies ahead in the exploratory synthesis of functional inorganic nitrides.…”