Steering Cu-Based CO₂RR Electrocatalysts’ Selectivity: Effect of Hydroxyapatite Acid/Base Moieties in Promoting Formate Production

Among all CO2 reduction reaction (CO2RR) active metals, copper is the only one that exhibits optimal *CO binding energy for multiple electron transfers. Despite such a unique feature, the use of Cu-based CO2RR catalysts at the industrial scale is hampered by large overpotentials and poor selectivity. In this realm, the introduction of acidic/basic functionalities at the catalyst surface may help to both overcome scaling relations (i.e., lower CO2RR overpotential) and tune the selectivity of Cu-based catalysts. Herein, we demonstrate that an amphoteric calcium phosphate additive (hydroxyapatite, HAP, Ca10(PO4)6(OH)2) alters the product distribution from Cu-based catalysts by steering CO2RR selectivity toward liquid oxygenated products, promoting formate production over CO.