Design and tuning of molecular iron complexes for electrocatalytic ammonia oxidation

Abstract

The goal of using ammonia as a solar fuel motivates the development of selective ammonia oxidn. (AO) catalysts for fuel cell applications. We are developing mol. catalysts for this process using earth-abundant iron and have found that [(TPA)Fe(NH₃)₂]²⁺ has high activity for electrochem. AO. We detail our latest efforts to improve upon Fe-mediated AO electrocatalysis by designing new catalyst structures that require less applied bias while also enhancing the catalytic rate, contrary to the typical relationship between overpotential and activity. To probe overpotential-activity relationships, we have investigated electronic and structural perturbations to the TPA auxiliary ligand, while maintaining its imposed cislabile coordination geometry. We present these results alongside detailed electrochem. mechanistic data buttressed by theor. investigations, including our most recent data related to the key N-N bond-forming step.