Defect-Engineered N-Doped Graphene Oxide-ZnWO4 Nanocuboids: Advancing Oxygen Reduction and Photo-Assisted Methanol Oxidation Reactions.

The development of direct methanol fuel cells (DMFCs) relies on designing replacements for benchmark platinum (Pt)-based electrocatalysts toward methanol oxidation reaction (MOR) that exhibit high resistance to CO poisoning, improve kinetic sluggishness, devoid of unwanted intermediates, low catalyst cost, and wide operating conditions. This study presents the development of defect engineering N-doped graphene oxide (NG) supported ZnWO4 nanocuboids as an efficient catalyst for photoelectrochemical MOR and electrochemical ORR. Under visible light (420 nm), the NG/ZnWO4 nanohybrid exhibits exceptional photoelectrochemical MOR with low potential of 0.5V with a high oxidation peak current density of ≈10 mA cm-2 is recorded while comparing with benchmark catalyst Pt/C. In two electrode systems for DMFC, the catalyst reaches an impressive maximum power production of 111 mW cm-2 with very stable charge-discharge cycles of 0.33 mV cycle-1, which is far superior to ZnWO4's alone. Simultaneously, the nanocomposite exhibits excellent ORR activity in alkaline medium with improved onset half-wave potential of 0.85V, high current density of 5.8 mA cm-2 at 1600 rpm, and robust stability, attributed to the synergistic effect between NG and ZnWO4. This work has reinforced these findings with theoretical insights using the Vienna Ab initio Simulation Package (VASP) to assess both PMOR and ORR performance and reaction intermediates.