High entropy spinel oxide for efficient electrochemical oxidation of ammonia

Ammonia has emerged as a promising energy carrier owing to its carbon neutral content and low expense in long-range transportation. Therefore, development of a specific pathway to release the energy stored in ammonia is therefore in urgent demand. Electrochemical oxidation provides a convenient and reliable route to attain efficient utilization of ammonia. Here, we report that the high entropy (Mn, Fe, Co, Ni, Cu)₃O₄ oxides can achieve high electrocatalytic activity for ammonia oxidation reaction (AOR) in non-aqueous solutions. The AOR onset overpotential of (Mn, Fe, Co, Ni, Cu)₃O₄ is 0.70 V, which is nearly 0.2 V lower than that of their most active single metal cation counterpart. The mass spectroscopy study reveals that (Mn, Fe, Co, Ni, Cu)₃O₄ preferentially oxidizes ammonia to environmentally friendly diatomic nitrogen with a Faradic efficiency of over 85%. The X-ray photoelectron spectroscopy (XPS) result indicates that the balancing metal d-band of Mn and Cu cations helps retain a long-lasting electrocatalytic activity. Overall, this work introduces a new family of earth-abundant transition metal high entropy oxide electrocatalysts for AOR, thus heralding a new paradigm of catalyst design for enabling ammonia as an energy carrier.