A Tandem (Bi₂O₃ → Bi_met) Catalyst for Highly Efficient ec-CO₂ Conversion into Formate: Operando Raman Spectroscopic Evidence for a Reaction Pathway Change

Abstract

A novel bismuth oxide nanofoam, produced by means of the dynamic hydrogen bubble template (DHBT) electrodeposition approach followed by thermal annealing at 300 °C for 12 h, demonstrates excellent electrocatalytic selectivity toward formate production with faradaic efficiencies (FEs) never falling below 90% within an extended potential window of ∼1100 mV (max. FE formate = 100% at −0.6 V vs RHE). These promising electrocatalytic characteristics result from the coupling of two distinct reaction pathways of formate formation in the aqueous CO 2 -sat. 0.5 M KHCO 3 electrolyte, which are active on (i) the partly reduced Bi 2 O 3 foam at low overpotentials (sub-carbonate pathway) and (ii) on the corresponding metallic Bi met foam catalyst at medium and high overpotentials (Bi−O pathway). For the first time, operando Raman spectroscopy provides experimental evidence for the embedment of CO 2 into the oxidic Bi 2 O 3 matrix (sub-carbonate formation) at low overpotentials prior to and during the CO 2 reduction reaction (CO 2 RR). The gradual transition of the formed carbonate/oxide composite catalyst into its fully metallic state is monitored by operando Raman spectroscopy as a function of electrolysis time and applied potential. The observed structural and compositional alterations correlate with changes in the faradaic efficiency and partial current density of formate production (PCD formate ), which reaches a maximum value of PCD formate = −84.1 mA cm −2 at −1.5 V vs RHE. The so-called identical location scanning electron microscopy technique was applied to monitor morphological changes that take place on the nanometer length scale upon sub-carbonate formation and partial electro-reduction of the oxidic precursor during the CO 2 RR. However, the macroporous structure of the foam catalyst remains unaffected by the (oxide/ carbonate → metal) transition and the catalytic CO 2 RR. KEYWORDS: ec-CO 2 reduction, operando Raman spectroscopy, identical location (IL) SEM, formate production, carbon fiber cloth, (BiO) 2 CO 3 , Bi 2 O 3 nanofoam

Insights from Operando and Identical Location (IL) Techniques on the Activation of Electrocatalysts for the Conversion of CO2: A Mini-Review

“…[19,20,28] The actual foam catalysts, being active towards alcohol and hydrocarbons, can therefore be considered as truly oxidederived (OD). [19] As a counter-example to that, we also discuss oxidized Bi foam catalysts [18] used for the highly selective production of formate. Our investigations reveal that both the oxidized as well as the corresponding metallic foams exhibit pronounced electrocatalytic activity towards the ec-CO 2 RR.…”

“…Finally, we hint at two ec-CO 2 RR pathways that are distinctly active on oxide-derived Cu and Bi 2 O 3 /Bi foam electrocatalysts. [18] 2. Experimental [18,19] Experimental details on the Cu and Bi foam preparation and the performed operando/IL investigations have already been detailed elsewhere.…”

“…[17] Herein we review and compare the structural, compositional and performance characteristics of two prototypical foam electrocatalysts that are based on Cu and Bi systems published recently. [11,[18][19][20] Among various materials studied so far, Cu stands out as the only known mono-metallic catalyst that can produce multiple hydrocarbons and alcohols of various chain lengths at elevated rates from the ec-CO 2 RR. [10,[21][22][23][24][25][26] In this context, C-C [13,19], with permission of the American Chemical Society.…”

Rational Design of 1D Porous Carbon Microtubes Supporting Multi‐size Bi2O3 Nanoparticles for Ultra‐long Cycle Life Lithium‐Ion Battery Anodes

“…In addition, all strong diffraction peaks of ms-Bi/CMTs and ms-Bi 2 O 3 /CMTs can be indexed to Bi (PDF#85-1330) and Bi 2 O 3 (PDF#78-1793), and the broad peak between 20°-25°is devoted to amorphous carbon peak, manifesting that target substances at each stage have been successfully synthesized. [24] As displayed in XRD of bare Bi 2 O 3 (Figure S3), there is no amorphous carbon peak, confirming that carbon has been absolutely decomposed. The bands at 90, 301 and 469 cm À 1 in the Raman spectrum (Figure 4b) illustrate the existence of Bi-O structure in ms-Bi 2 O 3 /CMTs.…”

Boosting CO2 electroreduction over Co nanoparticles supported on N,B-co-doped graphitic carbon

“…To date, the main catalysts used in the electrocatalytic CO 2 RR of CO 2 to CO include noble metals (Au, Ag, and Pd), 13–15 oxides (CuO, ZnO, and Bi 2 O 3 ), 16–18 chalcogenides (Cu 2 S, CdS, and MoS 2 ), 19–21 alloys (Pd–Ag, Co–Au, and Cu–Ru), 22–24 single-atom catalysts 25–28 and some carbon materials. 29–31 These catalysis processes can efficiently hinder the hydrogen evolution reaction (HER), which is competitive with CO 2 RR.…”