Robust Palladium Hydride (PdH/C) Catalyst for Electrocatalytic Formate Formation with Limited of CO Poisoning

Carbon dioxide capture, reduction, and valorization is of great importance to environmental conservation and green energy storage. Recent electrochemical CO₂ reduction exhibits the capability of converting CO₂ to various chemicals, which still face challenges such as high overpotential and low selectivity. The integration of electrocatalytic and biocatalytic cascade systems is able to provide substantial opportunities for CO₂ conversion.¹ But the selection of electrocatalysts needs more specific requirements such as low overpotential and high selectivity. Meanwhile, formate, serves as a major product of CO₂ electroreduction and feedstock for subsequent biocatalytic processes, possesses highest normalized price (16.1 $ / electron) among all products², demonstrating its high practical application value. Pd stands out from many catalysts because of its unique electrochemical CO₂ reduction to formate properties such as that it can selectively produce formate at equilibrium potential.³ Inevitably produced CO, however, poisons and deactivates the surface of Pd, resulting in insufficient operating lifetime for traditional Pd.^4–9 Herein, we will present our current research into Pd hydride nanoparticles (PdH/C) derived by using one-step solvothermal synthesis technique¹⁰ for formate production over potential ranges from 0V to -0.6V (vs RHE) that this large potential range selective for formate attribute to the insertion of hydride into the Pd lattice, promoting the electrohydrogenation process on the surface. This catalyst conducts a ~92% faradaic efficiency for formate at -0.4V (vs RHE) with current density as high as 5 mA/cm² in H-cell, which provides a yield over 1600 μmol/h/mg_pd. The working life at -0.4V (vs RHE) reaches a record of 4 hours, which is ~15 times longer than a commercial Pd, outperforming all previously reported Pd catalysts in electrosynthesis of formate from CO₂. This high CO tolerance attribute to relative weak CO adsorption strength with the presence of α&β hydride. A practical method of removing toxic CO from the surface by applying a positive potential shock has shown promising results, avoiding the unrealistic exposure of the catalyst to air. By alloying PdH with earth abundant element Cu, the faradaic efficiency, production, and stability of formate has been further improved. In addition, a Cu-based catalyst with high selectivity to methanol (~77%) will be presented¹¹, which can also be applied into the hybrid cascade system to convert CO₂ into higher reduced products.

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