The selectivity and activity of the carbon dioxide reduction (CO 2 R) reaction are sensitive functions of the electrolyte cation. By measuring the vibrational Stark shift of in situ-generated CO on Au in the presence of alkali cations, we quantify the total electric field present at catalytic active sites and deconvolute this field into contributions from (1) the electrochemical Stern layer and (2) the Onsager (or solvation-induced) reaction field. Contrary to recent theoretical reports, the CO 2 R kinetics does not depend on the Stern field but instead is closely correlated with the strength of the Onsager reaction field. These results show that in the presence of adsorbed (bent) CO 2 , the Onsager field greatly exceeds the Stern field and is primarily responsible for CO 2 activation. Additional measurements of the cation-dependent water spectra using vibrational sum frequency generation spectroscopy show that interfacial solvation strongly influences the CO 2 R activity. These combined results confirm that the cation-dependent interfacial water structure and its associated electric field must be explicitly considered for accurate understanding of CO 2 R reaction kinetics.

Site-specific vibrational probes were used to elucidate the interfacial solvation structure between catalytic active sites and inactive sites on a Au electrode to reveal a unique, opposing cation-dependent double layer structure at active sites.

We investigate amplified energy transfer in conjugated polymer nanoparticles (CPNs or Pdots) by studying both fluorescence quenching of CPN donors and the sensitization of reactive dye acceptors. By delivering excitation energy to dye dopants via a combination of Forster energy transfer and exciton diffusion, CPNs act as powerful light-harvesting antennae. This phenomenonamplified energy transferis used to sensitize dye dopants, producing a higher concentration of the dye's excited state than would be observed upon direct excitation. Here, we study CPN sensitization of a low-efficiency photochemical reaction to determine the CPN size and dye loading that yield optimized outputs in the form of energy transfer efficiency, the antenna effect (AE), and reaction duration. Our model system is the cycloreversion reaction of a diarylethene (DAE) photochrome as the dye dopant and CPNs of the conjugated polymer poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-1,4-benzo-{2,1′-3}-thiadiazole] as the sensitizer. In their visible-absorbing form, DAE dyes are localized on the particle surface and are effective fluorescence quenchers of 15, 20, and 26 nm diameter CPNs. Quenching is most efficient for the smallest particles, and high dye loadings are necessary to offset reduced efficiency as CPN size increases. Our photokinetic studies of DAE acceptors demonstrate the crucial importance of dye loading: both energy transfer efficiency and the AE show abrupt declines when the dye concentration is increased beyond a critical threshold. We find that CPNs with a 15 nm diameter exhibit the most efficient energy transfer (99−100%) and the largest AE (32) of the CPNs studied. For CPNs of all sizes and dye loadings, a photoselection phenomenon reveals that the energy-transferaccepting ability of the DAE dyes varies tremendously within the dye ensemble. These findings are used to develop design recommendations for CPN sensitizers.

The electrochemical conversion of CO2 represents a promising way to simultaneously reduce CO2 emissions and store chemical energy. However, the competition between CO2 reduction (CO2R) and the H2 evolution reaction...