Low-cost synthesis of non-noble Ni-based MXene (Ni3C) nanosheets decorated nickel foam as a bifunctional electrocatalyst for alkaline-acid urea-nitrate fuel cell

Urea and nitrate are the two indispensable hydrogen generation molecules present in different biological and non-biological sources like human urine, wastewater, groundwater samples. These molecules can be removed via urea oxidation reaction (UOR) and nitrate reduction reaction (NRR) while using them as a source for direct urea fuel cells (DUFCs) and direct nitrate fuel cells (DNFCs), respectively. Herein, we report the nickel-based MXene (Ni3C) nanosheets modified 3D skeletal nickel foam (Ni3C/NF) as a bifunctional catalyst electrode for DUFC and DNFC in alkaline and acid electrolytic medium, respectively. The high purity synthesis of Ni3C nanosheets is achieved through a solid-state synthesis of Ni-based MAX compound (Ni3AlC2) followed by an etching and exfoliation process (via solvothermal technique). The as-fabricated Ni3C/NF electrode exhibits a peak current density of 434 mA/cm2 (for UOR) and 85 mA/cm2 (for NRR) at an onset potential of ∼0.62 V (vs Hg/HgO) and ∼-0.58 V (vs Hg/HgO), respectively. This performance of the electrode is ascribed to the improved electrocatalytic activity of Ni3C nanosheets with good chemical stability and large surface area for UOR and NRR. This excellent bifunctional performance of the catalyst electrode proves the efficacy of the Ni3C nanosheets-based electrode for direct fuel cell applications.