Abstract
In this work, we employ differential electrochemical mass spectrometry (DEMS) to track the real-time evolution of CO at nanoporous gold (NpAu) catalysts with varying pore parameters (diameter and length) during the electrochemical CO2 reduction reaction (CO2RR). We show that due to the increase in the local pH with increasing catalyst roughness, NpAu catalysts suppress the bicarbonate-mediated hydrogen evolution reaction (HER) compared to a flat Au electrode. Additionally, the geometric current density for CO2RR increases with the roughness of NpAu catalysts, which we attribute to the increased availability of active sites at NpAu catalysts. Together, the enhancement of CO2RR and the suppression of competing HER results in a drastic increase in the faradaic selectivity for CO2RR with increasing pore length and decreasing pore diameter, reaching near 100% faradaic efficiency for CO in the most extreme case. Interestingly, unlike the geometric current density, the specific current density for CO2RR has a more complicated relation with the roughness of the NpAu catalysts. We show that this is due to the presence of ohmic drop effects along the length of the porous channels. These ohmic drop effects render the pores partially electrocatalytically inactive and hence, they play an important role in tuning the CO2RR activity on nanoporous catalysts.
Highlights
In this work we studied the role of pore parameters in tuning the activity/selectivity of electrochemical CO2 reduction reaction (CO2RR)
In going from NpAu1 to NpAu4 the pore diameter decreases and the pore length increases. This in turn leads to decreasing “effective diffusion” through the porous channels due to the generation of additional diffusional gradients along the length of the pores. This has already been studied in detail by the means of scanning electrochemical microscopy (SECM) where it was shown that the effective diffusion coefficient of any species (Deff = P′D; where P′ is porosity of the catalyst corrected by its tortuosity τ and D is the diffusion coefficient of the species in the solution phase) increases with increasing coarsening of the nanoporous Au (NpAu) catalysts.[40]
We studied the role of pore parameters in tuning CO2RR on nanoporous Au (NpAu) catalysts by using the online differential electrochemical mass spectrometry (DEMS) technique
Summary
Electrochemical reduction of CO2 (CO2RR) can be used to achieve a carbon-neutral energy cycle wherein carbon-based fuels can be produced with net zero emissions by using renewable electricity.[1,2,3] at present, the economic feasibility of this reaction remains an issue, primarily due to its low energy efficiency in commonly employed bicarbonate electrolytes, especially at high current densities.[4,5] significant research efforts have been made towards optimizing the catalyst design as well as the reaction process conditions for achieving better CO2RR selectivities.[6,7,8,9] Recently, meso- or nanoporous electrocatalyst materials have emerged as an interesting strategy to tune the selectivity of CO2RR. Geometric current density for HER decreases in going from Flat Au to NpAu4 (as shown in Fig. 1e) and the enhancement in the CO2RR Faradaic efficiency with the increasing roughness of the NpAu catalysts can, at least in part, be attributed to the suppression of competing HER reaction.[21,22, 25]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
