Anderson-Type Polyoxometalate-Mediated Structural Engineering of Co-MOF Derivatives for Nitrate Valorization to Ammonia

Electrocatalytic nitrate reduction for ammonia synthesis (ENRA) has attracted increasing attention, as it offers a sustainable strategy for carbon emission reduction while realizing the resource utilization of nitrate pollutants. Nevertheless, the development of electrocatalysts with superior activity, high selectivity, and long-term stability for NO₃RR remains a critical challenge. Herein, we report three Anderson-type polyoxometalate (POM)-modified cobalt-based metal-organic framework (Co-MOF) derivatives, namely, Co-CNS/MMo₆ (M = Fe, Co, Ni) composites, which were fabricated via a facile standing method. The introduced POMs play a regulatory role: on the one hand, they modulate the morphology of Co-CNS to form flower-like cluster structures with a large specific surface area, and on the other hand, as electron-rich clusters, they facilitate interfacial electron transfer between POMs and Co-CNS, thereby boosting the NO₃RR catalytic performance. Notably, the Co-CNS/NiMo₆ composite exhibits exceptional NO₃RR activity, achieving a maximum Faradaic efficiency (FE) of 99.2% at -0.8 V versus the reverse hydrogen electrode (vs RHE) and a high NH₃ yield rate of 12.82 mg h⁻¹ mgcat.⁻¹, which is better than most previously reported MOF-based derivative catalysts. In situ spectroscopic measurements reveal that NH₃ formation follows a kinetically favorable pathway: NO₃⁻ → *NO₃ → *NO₂ + NO₂⁻ → *NO → *NH → *NH₂ → NH₄⁺. This work highlights the great potential of POM-modified MOF derivatives as high-performance electrocatalysts for electrochemical NO₃RR, providing a promising approach for the rational design of advanced ENRA catalysts.