Nano high-entropy oxide cathode with enhanced stability for direct borohydride fuel cells

Abstract

High-entropy materials have become high-activity electrocatalysis owing to their high-entropy effect and multiple active sites. Herein, we synthesize a series of carbon-supported nano high-entropy oxides (HEOs/C), specifically (PtFeCoNiCu)O/C, using a carbothermal shock (CTS) method for application as a cathode catalyst in direct borohydride fuel cells (DBFCs). The microstructure of the prepared catalysts was characterized by X-ray photoelectron spectroscopy, X-ray absorption fine structure, and transmission electron microscopy. The prepared (PtFeCoNiCu)O/C, with particle sizes ranging from 2 to 4 nm, demonstrates 3.94 transferred electrons towards the oxygen reduction reaction in an alkaline environment, resulting in a minimal H₂O₂ yield of 2.6%. Additionally, it exhibits a Tafel slope of 61 mV dec⁻¹, surpassing that of commercial Pt/C (82 mV dec⁻¹). Furthermore, after 40,000 cycles of cyclic voltammetry (CV) testing, the half-wave potential of (PtFeCoNiCu)O/C shows a positive shift of 3 mV, with no notable decline in the limiting current density. When (PtFeCoNiCu)O/C is used as a cathode catalyst in DBFCs, the DBFC achieves a maximum power density of 441 mW cm⁻² at 60 °C and sustains a cell voltage of approximately 0.73 V after 52 h at 30 °C. These findings confirm that HEO/C is a promising cathode catalyst for DBFCs.