Discovery of the role of GDL porosity in direct N2 fixation to NH3 using enhanced MnFe2O4/graphene-based photoelectrocatalytic devices

Finding a sustainable alternative to the energy-intensive Haber-Bosh process for ammonia (NH3) production remains a key challenge. In this paper, we explore the influence of GDL porosity on the NH3 formation rate, finding 38.4 µg h-1 cm-2 NH3 in the least porous and 282 µg h-1 cm-2 NH3 in the most porous. Furthermore, we report a photoelectrocatalytic (PEC) approach that achieves up to 90% Faradaic efficiency using MnFe2O4-based semiconductors. A graphene-MnFe2O4 photoelectrode achieves 292 µg h-1 cm-2 NH3 at low overpotential, -0.2 V vs Ag/AgCl/Cl-1 (3.0 M KCl). In contrast, an electrode without graphene achieves 48.8 µg h-1 cm-2 NH3, highlighting the key role of graphene. Furthermore, PEC technology demonstrates superior performance compared to photocatalytic and electrocatalytic modes using the same electrodes, highlighting the importance of rational device and electrode design. These results reinforce that high-efficiency N2 fixation depends on the interconnection between catalyst properties, electrode structure, and the type of photo/electrocatalytic technology, offering new perspectives for the development of scalable, solar-powered PEC systems for sustainable NH3 production.