Section S1: Materials and Electrolysis Cell Design Materials. Materials were purchased in the grade indicated and used as received. Ammonium carbonate ((NH4)2CO3, 99.999%), ammonium chloride (NH4Cl. BioUltra), ammonium hydroxide (NH4OH, BioUltra), ammonium perchlorate (NH4ClO4, 99.999%), ammonium sulfate ((NH4)2SO4, 99.999%), ammonium tetrathiomolybdate ((NH4)[MoS4], 99.97%), boric acid (H3BO3, BioUltra), chromium(III) sulfate monohydrate (Cr2(SO4)3•H2O, 99.999%), cobalt(II) acetate tetrahydrate (Co(OAc)2•4H2O, 99.999%), cobalt(II) chloride hexahydrate (CoCl2•6H2O, ACS 98%), cobalt(II) nitrate hexahydrate (Co(NO3)2•6H2O, 99.999%), copper(II) sulfate heptahydrate (CuSO4•5H2O, 99.995%), glycine (NH2CH2COOH, BioUltra), iridium(III) acetylacetonate (Ir(acac)3, 97%), iron(II) chloride tetrahydrate (FeCl2•4H2O, 99.99%), iron(III) chloride heptahydrate (FeCl3•6H2O, ACS 97%), iron(III) nitrate nonahydrate (Fe(NO3)3•9H2O, 99.99%), iron(II) sulfate heptahydrate (FeSO4•7H2O, ACS 99%), manganese(II) sulfate hydrate (MnSO4•H2O, 99.99%), nickel(II) nitrate hexahydrate (Ni(NO3)2•6 H2O, 99.999%), nickel(II) sulfate hexahydrate (NiSO4•6H2O, 99.99%),nickel(II) chloride hexahydrate (

16 crystalline metal oxide nanoparticulate systems are adhered to an electrode surface using a conventional drop-casting method and measured for their activity for the oxygen evolution reaction.

Carbon dots (C-dots) are often synthesized, modified, and studied as a mixture. Unfortunately, the spectroscopic and biological properties measured for such C-dots assume that there is a high degree of homogeneity in the produced sample. By means of high-resolution separation techniques, we show that "as-synthesized" C-dots exist as a relatively complex mixture and that an unprecedented reduction in such complexity can reveal fractions of C-dots with unique luminescence properties. The wavelength-dependent photoluminescence commonly assigned as an inherent property of C-dots is not present in fractionated samples. While ultraviolet-visible absorption profiles reported for C-dots are typically featureless, we have found fractions of C-dots possessing unique absorption bands, with different fractions possessing specific emission wavelengths. Furthermore, fractionated C-dots showed profound differences in emission quantum yield, allowing for brighter C-dots to be isolated from an apparent low quantum yield mixture. These more luminescent fractions of C-dots displayed improved biological compatibility and usefulness as cellular imaging probes.

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.