Suppressing H₂ Evolution and Promoting Selective CO₂ Electroreduction to CO at Low Overpotentials by Alloying Au with Pd

Abstract

CO 2 electroreduction is a promising technology to produce chemicals and fuels from renewable resources. Polycrystalline and nanostructured metals have been tested extensively while less effort has been spent on understanding the performance of bimetallic alloys. In this work, we study compositionally variant, smooth Au−Pd thin film alloys to discard any morphological or mesoscopic effect on the electrocatalytic performance. We find that the onset potential of CO formation exhibits a strong dependence on the Pd content of the alloys. Strikingly, palladium, a hydrogen evolution catalyst with reasonable exchange current density, suppresses hydrogen evolution when alloyed with gold in the presence of CO 2 . Cyclic voltammetry, in situ surface enhanced infrared absorption spectroscopy, and potential-dependent online product analysis strongly suggest that by alloying Au with Pd a significant increase in the surface coverage of adsorbed CO occurs with increasing Pd content at low overpotentials (e.g., approximately −0.35 V vs RHE). Such an increase in CO coverage suppresses H 2 evolution due to the lack of vacant active sites. Moreover, the overall increase in the binding energy with the CO 2 intermediates gained with the addition of Pd increases the CO production at low overpotentials, where polycrystalline Au suffers from poor CO 2 adsorption and poor selectivity for CO production. These results show that promising CO 2 reduction electrode materials (e.g., Au) can be alloyed not only to tune the catalyst's activity but also to deliberately decrease the availability of surface sites for competitive H 2 evolution.

Copper-indium bimetallic catalysts for the selective electrochemical reduction of carbon dioxide

“…Currently, precious metals such as gold and palladium can effectively convert CO2 into CO or formate [19][20][21][22]; however, their high cost greatly limits their application in CO2RR. Indium and its alloys have already been proven to possess high catalytic properties for CO2RR to afford formate with a low cost [23][24][25][26][27][28][29]. However, the current density and selectivity of these catalysts are unsatisfactory at low overpotentials.…”

Progress in development of electrocatalyst for CO2 conversion to selective CO production

“…Lately, Pd alloyed with Au has shown that the Au 75 Pd 25 alloy can increase the adsorbed CO surface coverage coupled with decreasing the vacant active sites for HER at lower applied potentials, leading to the favorable selectivity for CO production. 84 In this regard, the J CO on the Au-rich alloy was higher than that of Au for all applied potentials. Meanwhile, Au-Pd core-shell nanoparticles fabricated from an Au-Pd alloy core and an ultrathin Pd-rich shell were reported to activate CO 2 -to-CO conversion in another study ( Figure 6E).…”

“…The addition of Cu to Pd has been shown to not only modulate the electronic structure and generate weaker binding of the CO to prevent CO poisoning of the Pd catalyst, but to change bond lengths of metallic atoms to decrease binding energy of hydrogen, which is beneficial for CO evolution. Lately, Pd alloyed with Au has shown that the Au 75 Pd 25 alloy can increase the adsorbed CO surface coverage coupled with decreasing the vacant active sites for HER at lower applied potentials, leading to the favorable selectivity for CO production . In this regard, the J CO on the Au‐rich alloy was higher than that of Au for all applied potentials.…”

Improving the Catalytic Activity of Carbon‐Supported Single Atom Catalysts by Polynary Metal or Heteroatom Doping

“…[ 40,41 ] Alloying not only reduces the required amount of precious metals but also optimizes the geometric and electronic structure of metals sites [ 42 ] which is beneficial for improving activity and selectivity. [ 43–45 ] For example, for different Pd alloys with Ag, Cu, or Ni, etc. the alloying Pd with Ag can promote the electrochemical conversion of CO 2 to syngas due to the appropriate adsorption strength of intermediates on Pd–Ag alloy.…”