Reduction of carbon dioxide in aqueous electrolytes at single-crystal MoS 2 or thin-film MoS 2 electrodes yields 1-propanol as the major CO 2 reduction product, along with hydrogen from water reduction as the predominant reduction process. Lower levels of formate, ethylene glycol, and t-butanol were also produced. At an applied potential of -0.59 V versus a reversible hydrogen electrode, the Faradaic efficiencies for reduction of CO 2 to 1-propanol were ~3.5% for MoS 2 single crystals and ~1% for thin films with low edge-site densities. Reduction of CO 2 to 1-propanol is a kinetically challenging reaction that requires the overall transfer of 18 e -and 18 H + in a process that involves the formation of 2 C-C bonds. NMR analyses using 13 CO 2 showed the production of 13 C-labelled 1-propanol. In all cases, the vast majority of the Faradaic current resulted in hydrogen evolution via water reduction. H 2 S was detected qualitatively when single-crystal MoS 2 electrodes were used, indicating that some desulfidization of single crystals occurred under these conditions.
The electro-oxidation of formate (HCOO − ) on polycrystalline Pt in highly basic medium (pH = 14) has been investigated by cyclic voltammetry, differential electrochemical mass spectrometry, potential step-linear sweep voltammetry, and adsorbate stripping experiments. Low oxidation currents were observed for HCOO − oxidation indicating that HCOO − is only weakly active under these conditions. The activity of HCOO − is confined to low potentials (0.2 V < E < 0.7 V vs RHE). Our results suggest a dual pathway mechanism for HCOO − oxidation, analogous to HCOOH oxidation in acid. In the case of HCOO − oxidation, the direct and indirect pathway analogues are referred to as the primary and secondary pathways, respectively. Formation of CO ads from HCOO − was observed to be slow. We also find that oxidation of CO ads (the secondary pathway) is strongly coupled to the oxidation of HCOO − through the primary pathway. Moreover, the oxidation of CO ads did not appreciably enhance HCOO − oxidation through the primary pathway, signifying the presence of other inhibitory processes such as OH adsorption. Adsorbate stripping experiments revealed, in addition to CO ads , the presence of a stable adsorbate that can undergo oxidation. We also find that the latter can be converted to CO ads in the H upd region. On the basis of the results obtained, a tentative mechanism of HCOO − oxidation in basic media is proposed.
The spatial variation in the photoelectrochemical performance for the reduction of an aqueous one-electron redox couple, Ru(NH 3 ) 6 3+/2+ , and for the evolution of H 2 (g) from 0.5 M H 2 SO 4 (aq) at the surface of bare and Pt-decorated p-type WSe 2 photocathodes has been investigated in situ using scanning photocurrent microscopy (SPCM). The measurements revealed significant differences in the charge-collection performance (quantified by the values of external quantum yields, Φ ext ) on various macroscopic terraces. Local spectral response measurements indicated a variation in the local electronic structure among the terraces which was consistent with a non-uniform spatial distribution of sub-band-gap states within the crystals. The photoconversion
Experimental
Sample preparation a) Single crystals of MoS 2Natural and synthetic crystals of MoS 2 were purchased from 2D semiconductors (El Cerrito, CA, USA) and Structure Probe Inc. (West Chester, PA). The doping and impurities of the purchased crystals were not known. To obtain crystals of uniform quality and doping, n-doped MoS 2 single crystals were synthesized in our laboratory by a chemical-vapor transport (CVT) technique.
Comparison of S 11 and S 11As noted in the manuscript we preferably use the S 11 = dS 11 dV data channel as opposed to the raw S 11 signal, primarily due to the robustness of S 11 (as all values here are complex unless otherwise noted, the tilde has been dropped). Shown in Figure S1 is a comparison of these data channels. Figure S1(a-b) shows the raw and unprocessed S 11 data, corresponding to the V b = 0 V image in Figure 2 (real and imaginary components are calculated from the amplitude and phase channels acquired). The S 11 signal remains stable, showing little drift in either signal or noise. In contrast, the simultaneously acquired unprocessed S 11 channels (c,d) show significant drift in both amplitude
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.