Synthesis and Characterization of Degradation‐Resistant Cu@CuPd Nanowire Catalysts for the Efficient Production of Formate and CO from CO₂

Abstract

Not only are the product selectivity and the activity of electrocatalysts important aspects for the evaluation of their overall performance, but also their stability and resistance against structural and compositional degradation during the electrocatalytic reaction. Palladium nanoparticles (Pd‐NPs) have already been identified as superior electrocatalysts for the electrochemical conversion of CO2 into formate at extremely low overpotentials and into carbon monoxide (CO) at medium overpotentials. However, these catalysts suffer from fast degradation, owing to irreversible CO poisoning of Pd reaction sites. Herein, we report on nanoparticulate bimetallic Pd45Cu55 catalysts, demonstrating a similar selectivity and activity to the pure Pd‐NPs, but showing additional superior degradation stability and resistance against CO poisoning. Pd45Cu55 catalysts were synthesized by means of a galvanic displacement reaction using copper nanowires (Cu‐NWs) as the starting material (template) for the galvanic displacement reaction, which leaves a surface‐confined alloy film and respective nanoparticles on the Cu‐NW template (denoted as Cu@CuPd‐NWs). A faradaic efficiency (FE) up to FEformate ≈80 % can be achieved at −0.3 V vs. RHE, thus clearly proving that the ‘anomalous’ CO2 reaction mechanism via the CO2 hydrogenation pathway, discussed for pure Pd‐NPs, can also be transferred to Pd‐based bimetallic systems. At medium overpotentials, the product selectivity changes from selective formate to predominant CO formation with a maximum faradaic efficiency of FECO=86 %. Extended CO2 electrolyses demonstrate, for both formate and CO production, superior degradation stability, for example, FECO remains at 85 %±5 % for the duration of 20 h. For the first time, identical location high‐angle annular dark‐field scanning transmission electron microscopy (IL‐HAADF‐STEM) in combination with energy‐dispersive X‐ray spectrometry and identical location scanning electron microscopy (IL‐SEM) were applied to demonstrate the compositional and structural stability of the bimetallic catalyst under CO2 reduction conditions.

Phase‐Dependent Electrocatalytic CO2 Reduction on Pd3Bi Nanocrystals

“…Corresponding Faradaic efficiency is derived to be >90 % across the examined working potential regime with the highest value close to unity. It is worth highlighting here that the capability of our Pd 3 Bi‐IMA to selectively and stably catalyze CO 2 RR to formate under η >0.2 V is truly remarkable and superior to many other Pd‐based catalysts reported in literature [26, 33–35] . By stark contrast, pure Pd nanocrystals exhibit much inferior chronoamperometric stability as expected (Figure S5) [24] .…”

Mesoporous PdAg Nanospheres for Stable Electrochemical CO2 Reduction to Formate

“…0.03 V) with initial Faradaic efficiency of ~75%. The selectivity quickly increases to and maintains >90% between -0.1 V and -0.3 V before HER starts to take off at <-0.3 V. Compared to the large majority of Pd-based materials reported in literature, [25,[33][34][35][36][37] it is remarkable that our PdAg_2 can enable CO 2 RR to formate with higher selectivity close to unity at lower overpotential (Figure 3d). We attribute such a high performance to the effective alloying between Pd and Ag as well as the three-dimensional mesoporous structure exposing large surface areas.…”

Alloyed Palladium–Silver Nanowires Enabling Ultrastable Carbon Dioxide Reduction to Formate

“…The combination of improved formate selectivity and remarkable stability even at intermediate overpotentials (where people previously believed that formate could not be stably formed on Pd) renders our electrocatalysts superior to other Pd‐based CO 2 RR materials. [ 30,32,40,47–52 ] It again highlights the advantageous synergy between Pd and Ag in alloy nanowires.…”