Electroactive coupling of formate dehydrogenase with Ni-modified triazine frameworks for efficient and selective CO2 photoreduction

Abstract

Developing an efficient and selective catalyst for solar-driven CO2 conversion remains a critical challenge owing to the high thermodynamic stability and sluggish reduction kinetics of CO2. Herein we report a robust bio-inspired enzyme-semiconductor hybrid photocatalyst fabricated via electroactive immobilization of formate dehydrogenase (Fatedh) onto Ni-decorated-nitrogen-deficient mesoporous triazine frameworks (Ni-mpg-C3Nx) for selective CO2 reduction. The integrated Ni atomic sites act as redox intermediaries to accelerate the interfacial electron transfer while nitrogen vacancies assist with the reactant adsorption and chemical activation process. Isothermal titration calorimetry (ITC) reveals exceptionally strong enzyme-support affinity, yielding low dissociation constant (Kd) ranging from 9.33 & times; 10-7 to 8.15 & times; 10-7. The electroactive coupling promotes efficient NAD+/NADH regeneration, facilitating the enzymatic CO2 conversion at the active Mo/W catalytic center of Fatedh. Consequently, the optimized photocatalyst Ni-mpg-C3Nx_Fatedh achieves a remarkable formic acid yield of 6.8 mmol, which is 4.5-fold improvement over mpg-C3Nx_Fatedh (1.5 mmol) and a 7-fold enhancement compared to that of bare mpg-C3N4 with a TOF of 9.36 & times; 105 s-1. Kelvin probe force microscopy (KPFM) demonstrates an elevated surface potential (similar to 4000 & micro;V) that plays a vital role in suppression of charge recombination and improves the charge carrier mobility across the bio-inorganic heterointerface. Notably, the hybrid photocatalyst is stable and highly selective for CO2 reduction under ambient conditions, without requiring an inert atmosphere, offering pathways towards sustainable solar fuel production.