PtxAg100−x nano-alloy decorated N-doped reduced graphene oxide: a promising electrocatalyst for direct urea fuel cells

Abstract

Direct urea fuel cells (DUFCs) offer an environmentally friendly, and cost-effective way to turn wastewater into energy. However, the paucity of efficient, cost-effective, and electrochemically stable urea electro-oxidation reaction (UOR) specific electrocatalysts continues to impede the design and development of practically useful DUFCs. The present work explores the design and development of N-doped graphene (NGr)-supported platinum (Pt) plus silver (Ag) alloy nanohybrids (Pt_xAg_100−x-NGr) as potential UOR electrocatalysts. Our results suggest that the electrocatalytic performance of Pt_xAg_100−x-NGr is very sensitive toward the composition of this nanohybrid. The nanohybrid with a Pt : Ag ratio of 1 : 1, referred to as Pt₅₀Ag₅₀-NGr in the MS, exhibits the best UOR electrocatalytic performance. The Pt₅₀Ag₅₀-NGr composite exhibits a Tafel slope of just ∼12.92 mV dec⁻¹, and a UOR-specific activity of nearly 4028 mA cm⁻² mg cat⁻¹ at 1.673 V (vs. RHE) and requires an overpotential of just 1.617 V (vs. RHE) to maintain a UOR specific current density of 10 mA cm⁻². These parameters qualify the Pt₅₀Ag₅₀-NGr as a promising anode material for DUFCs. This we demonstrate through the design of a Pt₅₀Ag₅₀-NGr anode-based prototype urea-H₂O₂ fuel cell that delivers an open circuit voltage (OCV) of 750 mV and a power density of ∼5.75 mW cm⁻².