Synergistic sulfur-doped tri-metal phosphide electrocatalyst for efficient hydrazine oxidation in water electrolysis: Toward high-performance hydrogen fuel generation

Abstract

Replacing the slow anodic oxygen evolution reaction with the hydrazine (N2H4) oxidation reaction (HzOR) is a promising strategy for achieving energy-efficient hydrogen (H2) fuel production in water electrolyzer systems. Therefore, developing efficient electrocatalysts for the HzOR, in combination with the cathodic hydrogen evolution reaction, is essential for achieving high H2 fuel generation rates and advancing N2H4 fuel cell technology. In this study, we fabricated NiCoFe oxide derived from a metal-organic framework, followed by the physical mixing and carbonization of S and P. The strong intrinsic activity of S-doped tri-metal phosphide (TMP) against the HzOR is evidenced by its role in the chemisorption of N2H4 on its surface, where a dative link is formed between the electrons of the lone pair of nitrogen atoms in N2H4 and the empty orbitals of the metals in the TMP alloy. Using this process, we demonstrated the high performance of flow cell electrolysis for overall water and hydrazine oxidation by assembling the S-TMP||S-TMP electrode as both the anode and cathode of the electrolyzer. The resulting cell voltage was 0.35 V for HzOR and 1.53 V for overall water splitting, and the electric current density reached 10 mA·cm−2, with high stability over 20 h. The electrolyzer efficiency was significantly superior to that of electrolyzers constructed using other types of dual-purpose electrocatalysts as catalyst pairs. Furthermore, the overall effectiveness of the electrolyzer was comparable to that of electrolyzers incorporating two distinct, well-established, single-purpose electrocatalyst pairs for the water and hydrazine splitting reactions.