Charge Manipulation of Porous Coordination Cages Tunes the Efficiency and Selectivity in Electrochemical Synthesis

Electrocatalytic synthesis of high-value chemicals has been attracting growing interest owing to its environmentally benign reaction pathways. Among these processes, the electrocatalytic reduction of nitrate (NO3-) to ammonia (NH3), known as NO3RR, and the oxidation of 5-hydroxymethylfurfural (HMFOR) stand out as two cornerstone reactions; yet, their efficiency and selectivity pose ongoing challenges. In this study, we introduce a charge manipulation approach for the design of highly efficient electrocatalysts tailored for the simultaneous coupling of NO3RR and HMFOR. We have synthesized a range of porous coordination cages (PCCs) that share the same topology and Co/Ni metal centers but incorporate different charged moeities, imparting them with distinct surface net charges. Electrocatalytic evaluations revealed that PCC-Co demonstrated a voltage-dependent activity in NO3RR. Conversely, PCC-Ni exhibited a precisely adjustable product selectivity in HMFOR, contingent upon the cage's charge state. In-situ analysis and Density functional theory (DFT) calculations underscored the profound impact of catalyst charge on the differential adsorption of reaction intermediates and the lowest free energy change (ΔG) during the pivotal reaction step, resulting in alterations to both activity and selectivity. These discoveries provide invaluable insights into the "structure-performance relationship" of NO3RR/HMFOR catalysts, highlighting PCCs as promising contenders for advanced electrocatalysts.