The
complexity of the electrocatalytic reduction of CO to CH4 and C2H4 on copper electrodes prevents
a straightforward elucidation of the reaction mechanism and the design
of new and better catalysts. Although structural and electrolyte effects
have been separately studied, there are no reports on structure-sensitive
cation effects on the catalyst’s selectivity over a wide potential
range. Therefore, we investigated CO reduction on Cu(100), Cu(111),
and Cu(polycrystalline) electrodes in 0.1 M alkaline hydroxide electrolytes
(LiOH, NaOH, KOH, RbOH, CsOH) between 0 and −1.5 V vs RHE.
We used online electrochemical mass spectrometry and high-performance
liquid chromatography to determine the product distribution as a function
of electrode structure, cation size, and applied potential. First,
cation effects are potential dependent, as larger cations increase
the selectivity of all electrodes toward ethylene at E > −0.45 V vs RHE, but methane is favored at more negative
potentials. Second, cation effects are structure-sensitive, as the
onset potential for C2H4 formation depends on
the electrode structure and cation size, whereas that for CH4 does not. Fourier Transform infrared spectroscopy (FTIR) and density
functional theory help to understand how cations favor ethylene over
methane at low overpotentials on Cu(100). The rate-determining step
to methane and ethylene formation is CO hydrogenation, which is considerably
easier in the presence of alkaline cations for a CO dimer compared
to a CO monomer. For Li+ and Na+, the stabilization
is such that hydrogenated dimers are observable with FTIR at low overpotentials.
Thus, potential-dependent, structure-sensitive cation effects help
steer the selectivity toward specific products.
The electrochemical conversion of carbon dioxide (CO 2 ) into valuable compounds is a promising route toward the valorization of this molecule of high environmental impact. Yet, an industrial process involving CO 2 electroreduction is still far from reality and requires deep and fundamental studies for a further understanding and better development of the process. In this work, we describe in situ spectroelectrochemical studies based on Fourier transform infrared spectroscopy and surface-enhanced Raman spectroscopy of the CO 2 reduction in acetonitrile solutions at copper electrodes. The influence of factors such as the water content and the supporting electrolyte on the reaction products were evaluated and compared to products obtained on metal electrodes other than Cu, such as Pt, Pb, Au, Pd, and Ag. The results show that at Cu electrodes in acetonitrile containing small amounts of water, the main reaction products from CO 2 reduction are carbonate, bicarbonate, and CO. The formation of CO was observed at less-negative potentials than the formation of (bi)carbonates, and the formation of carbonate and bicarbonate species appears to be the result of a reaction with electrochemically generated OH − from water reduction. In general, our experiments show the sensitivity of the CO 2 reduction reaction to the presence of water, even at the residual level.
Electrochemical CO2 reduction is an attractive option for storing renewable electricity and for the sustainable production of valuable chemicals and fuels. In this roadmap, we review recent progress in fundamental understanding, catalyst development, and in engineering and scale-up. We discuss the outstanding challenges towards commercialization of electrochemical CO2 reduction technology: energy efficiencies, selectivities, low current densities, and stability. We highlight the opportunities in establishing rigorous standards for benchmarking performance, advances in in operando characterization, the discovery of new materials towards high value products, the investigation of phenomena across multiple-length scales and the application of data science towards doing so. We hope that this collective perspective sparks new research activities that ultimately bring us a step closer towards establishing a low- or zero-emission carbon cycle.
The first part of this report studies the electrochemical properties of single-crystal platinum electrodes in acetonitrile electrolytes by means of cyclic voltammetry. Potential difference infrared spectroscopy in conjunction with linear voltammetry was used to obtain a molecular-level picture of this interface. The second part of this report studies the hydrogen evolution and the hydrogen oxidation reactions on the three low-index faces of Pt electrodes in acetonitrile electrolytes. The data (CVs and IR spectra) strongly suggest that acetonitrile and CN(-) molecules are adsorbed on single-crystal platinum electrodes in the range of -1.5 to 0.3 V versus Ag/AgCl. Those species block part of the adsorption sites for hydrogen adatoms, and they decompose on the surface in the presence of water. The nature of the cation and the presence of water strongly affect the onset of acetonitrile electrolysis and the kinetics and stability of the adsorbed species on the electrode. Finally, the hydrogen evolution and the hydrogen oxidation reactions on platinum single-crystal surfaces in acetonitrile electrolytes are strongly affected by the surface-energy state of Pt electrodes.
Bimetallic electrocatalysts
have emerged as a viable strategy to
tune the electrocatalytic CO2 reduction reaction (eCO2RR) for the selective production of valuable base chemicals
and fuels. However, obtaining high product selectivity and catalyst
stability remain challenging, which hinders the practical application
of eCO2RR. In this work, it was found that a small doping
concentration of tin (Sn) in copper oxide (CuO) has profound influence
on the catalytic performance, boosting the Faradaic efficiency (FE)
up to 98% for carbon monoxide (CO) at −0.75 V versus RHE, with prolonged stable performance (FE > 90%) for up to 15
h.
Through a combination of ex situ and in situ characterization techniques, the in situ activation
and reaction mechanism of the electrocatalyst at work was elucidated. In situ Raman spectroscopy measurements revealed that the
binding energy of the crucial adsorbed *CO intermediate was lowered
through Sn doping, thereby favoring gaseous CO desorption. This observation
was confirmed by density functional theory, which further indicated
that hydrogen adsorption and subsequent hydrogen evolution were hampered
on the Sn-doped electrocatalysts, resulting in boosted CO formation.
It was found that the pristine electrocatalysts consisted of CuO nanoparticles
decorated with SnO2 domains, as characterized by ex situ high-resolution scanning transmission electron microscopy
and X-ray photoelectron spectroscopy measurements. These pristine
nanoparticles were subsequently in situ converted
into a catalytically active bimetallic Sn-doped Cu phase. Our work
sheds light on the intimate relationship between the bimetallic structure
and catalytic behavior, resulting in stable and selective oxide-derived
Sn-doped Cu electrocatalysts.
Nanoparticle modified electrodes constitute an attractive way to tailor-make efficient carbon dioxide (CO2) reduction catalysts. However, the restructuring and sintering processes of nanoparticles under electrochemical reaction conditions not only impedes...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.