Multifunctional Coupled Co₃O₄/CuPc Heterojunction Enables Efficient Photoelectrocatalytic Nitrate-to-Ammonia Conversion

The photoelectrochemical (PEC) reduction of nitrate (NO3–) to ammonia (NH3) offers a sustainable approach for simultaneous wastewater remediation and green NH3 synthesis. However, current PEC catalysts face limitations in NH3 conversion efficiency and selectivity, significantly hindering their practical implementation. Herein, we developed a visible-light-responsive heterojunction catalyst composed of Co3O4 nanowires and copper phthalocyanine (CuPc) for selective NO3– to NH3 conversion. The Co3O4 nanowires provide abundant oxygen vacancy (acting as Lewis acid sites) and high surface areas, which synergistically enhance NO3– adsorption and activation. Meanwhile, the CuPc coating extends visible-light absorption and effectively suppresses the competing hydrogen evolution reactions (HER). The coherent interface between Co3O4 and CuPc not only promotes efficient charge separation but also stabilizes key reaction intermediates, achieving a 17-fold increase in NH3 yield (41.2 μg h–1 cm–2 at 0 V vs RHE) compared to pristine Co3O4. Density functional theory calculations demonstrate reduced energy barriers for the NO3– reduction pathway and suppressed HER activity at the heterojunction. This work underscores the potential of interfacial engineering in advancing catalytic systems for sustainable NO3– remediation and NH3 synthesis.