Constructing a crystalline–amorphous hydrated niobium pentoxide homojunction for superior photocatalytic CO2 reduction into CH4 with high selectivity

Abstract

The photocatalytic reduction of carbon dioxide (CO₂) into renewable fuels holds great promise as a sustainable energy production approach, addressing both the imminent energy crisis and global warming simultaneously. However, the poor CO₂ adsorption and rapid recombination of photogenerated charge carriers on semiconductors greatly limit the CO₂ conversion efficiency along with poor selectivity towards the desired product. Herein, we propose that the construction of a homojunction in a crystalline–amorphous photocatalyst can greatly enhance its photocatalytic performance. In this study, we developed a hydrated niobium pentoxide (HNBO) homojunction with co-existing crystalline and amorphous structures through a facile hydrothermal method. The resulting crystalline–amorphous HNBO demonstrated exceptional photocatalytic activity for CO₂ reduction into methane (CH₄) and carbon monoxide (CO), in which the selectivity for CH₄ reached 85.7%. The superior performance of HNBO can be attributed to the following factors: (i) the presence of a large specific surface area (355 m² g⁻¹) due to the aggregation of HNBO nanoparticles with abundant “ink bottle” mesopores, (ii) the abundant OH⁻ groups on HNBO promoting the adsorption and activation of CO₂, (iii) the enhanced separation of charge carriers resulting from the crystalline–amorphous homojunction interface, and (iv) a narrowed bandgap along with an elevated conduction band potential to give strong reduction power. This work presents a remarkable instance of a solitary crystalline–amorphous material for CO₂ photoreduction into CH₄ with superior activity and high selectivity. Notably, this was achieved without the need for any dopants or co-catalysts, underscoring the elegance of this photocatalyst.