(686f) Multimetallic Core-Shell Nanoporous Pd Alloys for Surface Poisoning Suppression during Electrohydrogenation of CO2 to Formate

The electrochemical reduction of CO₂ (CO2RR) has been extensively studied for making useful carbon based products e.g CO, formate/formic acid, alcohols etc., for renewable energy conversion and storage. There is variability in product selectivity¹, overpotential requirements and sustained activity depending upon binding affinities of catalyst surface with different reaction intermediates. Production of formate/formic acid as a CO2RR product is drawing focus because of its high energy density and utility as a chemical precursor. Traditional formate producing metals e.g. Co, In, Bi, Sn etc. require high overpotentials (>700 mV), limiting their energy effectiveness. Pd on the other hand, originally known to produce CO² at overpotentials above 600 mV RHE, has recently shown substantial formate FE’s at overpotentials below 200 mV⁴. However, the gradual poisoning of Pd-based CO2RR electrocatalysts through the slow production of CO, even at near unity formate FEs, results in deactivation of the catalyst surface³ and limits the viability of Pd for sustained electrolysis.

Here, we report synthesis of core-shell nanoporous bimetallic and trimetallic Pd (np-PdX, where X = Co, Ni, Cu, Ag, Cu-Sn, Cu-Ti) alloys that show suppressed CO deactivation based on the subsurface composition of the alloy electrocatalysts. The Pd skinned nanoporous alloys have been obtained by electrochemical dealloying⁵ where the presence of less noble metal/alloy under the Pd shell changes the electronic structure of the Pd and consequently alters the CO adsorption strengths and subsequent catalyst deactivation. The tortuous pores (pore size: 5 – 10 nm) give rise to roughness factors above 300 which generates high geometric formate partial current densities (> 30 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.

The suppression of surface poisoning is 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, as well as changes to the near surface hydrogen solubility which can also affect the adsorption strength of active/inactive intermediates and reaction selectivity. Thus np-PdX electrocatalysts based on a suitable choice of alloying component, exhibit high areal formate partial current densities and superior CO poisoning tolerance, demonstrating the utility of these materials for selective and stable CO₂ electrolysis.

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