Enhanced efficiency and durability of nickel sulfide catalyst integrated with reduced graphene oxide: Exploring hierarchically porous structures for methanol oxidation reaction

The growing demand for sustainable energy solutions highlights the need for advancements in electrocatalysts for direct methanol fuel cells (DMFCs). This study introduces a novel approach to enhance the efficiency and durability of nickel sulfide (NiS) catalysts. We developed a hierarchically porous structure integrated with reduced graphene oxide (rGO) on a nickel foam substrate. Using a dynamic hydrogen bubble template (DHBT) technique, we created a porous nickel scaffold. We then electrodeposited graphene oxide and NiS onto this scaffold, resulting in a hybrid structure termed NiS-rGO-Ni/NF. Characterization through SEM, XRD, and XPS confirmed that the catalyst has a highly porous structure with uniformly distributed Ni₃S₂ and Ni₃S₄ phases. The NiS-rGO-Ni/NF catalyst showed significant improvements over conventional NiS/NF. It achieved a peak current density of 84.10 mA/cm² in the presence of 0.1 M methanol, compared to 30.32 mA/cm² with NiS/NF. This enhancement is due to the porous nickel layer created using DHBT and the integration of rGO. Additionally, the NiS-rGO-Ni/NF catalyst demonstrated superior reaction kinetics, evidenced by a decrease in the Tafel slope from 204 mV/dec to 122 mV/dec. It also exhibited a remarkable increase in the electrochemically active surface area, reaching 179 cm² compared to 22 cm² for NiS/NF. These improvements in surface area and kinetics contribute to its excellent stability, with the catalyst maintaining consistent performance over 20 h of continuous operation. These results underscore the effectiveness of the NiS-rGO-Ni/NF catalyst in methanol oxidation and its potential for more efficient and stable electrochemical applications.