(544gm) Nanoporous Palladium Alloys As CO Poisoning Suppressing Electrocatalysts for Electrochemical Conversion of CO2 to Formate
Herein, we present making of free standing, core-shell, nanoporous Pd (np-PdX, where X = Ag, Cu, Ni, Co) alloys that display a compositional dependent CO deactivation rate. The np-PdX electrocatalysts are synthesized through electrochemical dealloying5 of 4 binary Pd15X85 (X = Co, Ni, Cu, Ag) alloys. Electrochemical dealloying drives the formation of Pd skinned nanoporous architectures where the presence of less noble metal under the Pd shell alters the electronic structure of the Pd skin and consequently affects the CO adsorption strengths thereby changing the rate of catalyst poisoning. The np-PdX electrodes have pore sizes ranging from 5 â 10 nm and a residual composition of ~ 30 atomic % of the less noble metal. The tortuous pores give rise to roughness factors above 500 which generates high geometric formate partial current densities (> 40 mA/cm2). Furthermore, the np-Pd electrodes are free standing and obviate the use of any binder and/or support which otherwise causes extra overpotential losses and morphological instability.
Upon performing extended electrolysis, the CO2RR activity, formate FE and degree of deactivation of the np-PdX elecrodes are compared with a traditional Pd/C electrocatalyst having particle sizes of 5-10 nm. While all the np-PdX electrodes show formate FE above 90% within 200 mV overpotential as already known for Pd/C, there is a significant dissimilarity in tolerance to CO poisoning as evidenced by the compositionally dependent time of deactivation. While np-PdAg and np-PdCu show faster deactivation compared to Pd/C, np-PdCo and np-PdNi suppress poisoning for much longer times. The results are explained on the basis of weakening of CO binding strengths due to electronic interactions of the alloying component that shifts the d-band center of Pd6. This is also shown by the trend of CO stripping peak potentials on Pd-skinned polycrystalline PdX (X = Co, Ni, Cu and Ag) alloys. Thus np-PdX electrocatalysts based on a suitable choice of alloying component, offer substantial suppression of CO poisoning, much higher formate geometric current densities and enhanced operational stability compared to traditional Pd based CO2RR electrocatalysts.
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