Photocatalytic conversion of carbon dioxide (CO₂) to hydrocarbons such as methanol makes possible simultaneous solar energy harvesting and CO₂ reduction, two birds with one stone for the energy and environmental issues. This work describes a high photocatalytic conversion of CO₂ to methanol using graphene oxides (GOs) as a promising photocatalyst. The modified Hummer's method has been applied to synthesize the GO based photocatalyst for the enhanced catalytic activity. The photocatalytic CO₂ to methanol conversion rate on modified graphene oxide (GO-3) is 0.172 μmol g cat⁻¹ h⁻¹ under visible light, which is six-fold higher than the pure TiO₂.

In this paper, we report a facile hydrothermal method to synthesize low-cost, high-catalytic-activity, and stable niobium-doped hexagonal tungsten trioxide nanowires (Nb-doped h-WO₃ NWs); these NWs were employed as catalysts to improve the electrocatalytic activity of graphite felt (GF) electrodes for use as positive electrodes in an all-vanadium redox flow battery (VRFB). The effect of Nb doping and its composition on the electrochemical performance of GF electrodes for a VRFB was investigated. Cyclic voltammetry and electrochemical impedance spectroscopy results showed that Nb-doped h-WO₃ NWs with a Nb/W atomic ratio of 0.03 exhibited the highest electrocatalytic activities for VO²⁺/VO₂ ⁺ couples among all the tested electrodes. This observation was attributed to the optimal Nb-doping concentration producing moderate defect states, thereby creating structural disorders, such as oxygen vacancies, in WO₃ and leading to the generation of more active sites for the VO²⁺/VO₂ ⁺ redox reaction on the electrode. Moreover, in charge–discharge tests, a VRFB single cell using the Nb-doped h-WO₃ NW (Nb/W = 0.03) catalyst demonstrated an excellent energy efficiency of 78.10% with a current density of 80 mA cm⁻². This efficiency is much higher than that demonstrated by VRFB cells with untreated GF (67.12%) and heat-treated GF obtained through the conventional method (72.01%). Furthermore, in the stability test of a VRFB single cell with the Nb-doped h-WO₃ NW (Nb/W = 0.03) catalyst, almost no decay of the cell was observed even after 30 cycles. This observation indicates the outstanding stability of the cell during the redox reaction of vanadium ions under highly acidic conditions.

Nonnoble metal catalysts are low-cost alternatives to Pt for the oxygen reduction reactions (ORRs), which have been studied for various applications in electrocatalytic systems. Among them, transition metal complexes, characterized by a redox-active single-metal-atom with biomimetic ligands, such as pyrolyzed cobalt–nitrogen–carbon (Co–N_x/C), have attracted considerable attention. Therefore, we reported the ORR mechanism of pyrolyzed Vitamin B12 using operando X-ray absorption spectroscopy coupled with electrochemical impedance spectroscopy, which enables operando monitoring of the oxygen binding site on the metal center. Our results revealed the preferential adsorption of oxygen at the Co²⁺ center, with end-on coordination forming a Co²⁺-oxo species. Furthermore, the charge transfer mechanism between the catalyst and reactant enables further Co–O species formation. These experimental findings, corroborated with first-principle calculations, provide insight into metal active-site geometry and structural evolution during ORR, which could be used for developing material design strategies for high-performance electrocatalysts for fuel cell applications.