Activation Matters: Hysteresis Effects during Electrochemical Looping of Colloidal Ag Nanowire Catalysts

Colloidal electrocatalysts are commonly synthesized using organic capping agents (surfactants), which control the size distribution and shape of the resulting nano-objects and prevent them from agglomerating during and after synthesis. However, the presence of a surfactant shell on the catalyst is detrimental, as the resulting performance of the electrocatalyst depends crucially on the ability of reactants to access active surface sites. Techniques for postsynthesis deprotection are therefore mandatory for removing the capping agents from the otherwise blocked reactions sites without compromising the structural integrity of the nanocatalysts. Herein, we present silver nanowires (Ag-NWs)produced via PVP-assisted polyol synthesis (PVP, polyvinylpyrrolidone)as effective catalysts for the electrochemical CO2 reduction reaction (ec-CO2RR), which reach Faradaic efficiencies close to 100% for CO formation after deprotection by a so-called “electrochemical looping” (ec-l) pretreatment. Electrochemical looping refers to a sequence of potentiostatic CO2 electrolysis experiments that exhibit well-defined starting (E start), vertex (E vertex), and end (E end) potentials. The resulting product distribution undergoes a profound hysteresis in the forward and corresponding backward run of the electrochemical looping experiment, thus pointing to an effective deprotection of the catalyst as made evident by postelectrolysis XPS inspection. These results can be considered as a prime example demonstrating the importance of the catalyst’s “history” for the resulting ec-CO2RR performance. These transient (non-steady-state) effects are crucial in particular for the initial stage of the CO2 electrolysis reaction and for catalyst screening approaches carried out on the time scale of hours.