Shape‐Controlled CO2 Electrochemical Reduction on Nanosized Pd Hydride Cubes and Octahedra

Electrochemical CO2 reduction reaction (CO2RR) provides a potential pathway to mitigate challenges related to CO2 emissions. Pd nanoparticles have shown interesting properties as CO2RR electrocatalysts, while how different facets of Pd affect its performance in CO2 reduction to synthesis gas with controlled H2 to CO ratios has not been understood. Herein, nanosized Pd cubes and octahedra particles dominated by Pd(100) and Pd(111) facets are, respectively, synthesized. The Pd octahedra particles show higher CO selectivity (up to 95%) and better activity than Pd cubes and commercial particles. For both Pd octahedra and cubes, the ratio of H2/CO products is tunable between 1 and 2, a desirable ratio for methanol synthesis and the Fischer–Tropsch processes. Further studies of Pd octahedra in a 25 cm2 flow cell show that a total CO current of 5.47 A is achieved at a potential of 3.4 V, corresponding to a CO partial current density of 220 mA cm−2. In situ X‐ray absorption spectroscopy studies show that regardless of facet Pd is transformed into Pd hydride (PdH) under reaction conditions. Density functional theory calculations show that the reduced binding energies of CO and HOCO intermediates on PdH(111) are key parameters to the high current density and Faradaic efficiency in CO2 to CO conversion. Pd cubic and octahedral nanoparticles dominated by Pd(100) and Pd(111) facets, respectively, are synthesized and evaluated for electrochemical CO2 reduction to synthesis gas. Experimental observations and density functional theory calculations demonstrate that the reduced binding energies of CO and HOCO intermediates on in situ formed PdH(111) correlate to the high current density and Faradaic efficiency in CO2 conversion.