ABSTRACT
We report the formation and characterization of one-dimensional chemical composition gradients of CdS on Au surfaces using bipolar electrodeposition. When an external electric field is applied across an electrically floating Au electrode immersed in a bipolar electrochemical cell, a position-dependent interfacial potential difference is generated along the length of the Au. This potential gradient can be used to induce variations of chemical composition within thin films electrodeposited onto the Au bipolar electrode (BPE). Thin films formed by bipolar electrodeposition represent continuous one-dimensional solid-state material libraries and were screened using resonance Raman microscopy and Auger electron spectroscopy. As predicted from simple thermodynamic considerations, we observed three distinct deposition zones scanning from the cathodic pole to the midpoint of the BPE: (i) CdS+Cd, (ii) stoichiometric CdS, and (iii) elemental S. Bipolar electrodeposition can be used to generate material libraries rapidly and without direct electrical contact to the substrate using extremely simple instrumentation.
ABSTRACT
We report on the influence of a series of transition-metal-substituted Wells-Dawson (P2W17MnO62(12-n)-; M = WVI, FeII, CoII, RuII) and Keggin (PW12O40(3-) and PCoW11O39(5-) anions on the oxygen reduction reaction (ORR) at Au, Pd, and Pt. Wells-Dawson POMs adsorbed on Au lead to large positive shifts of the ORR potential. The magnitude of the shift depends on the transition metal and is explained using a simple thermodynamic model. The best cathode performance was achieved using a PCoW11O39(5-) cocatalyst and a Pt cathode. The +54 mV positive shift in the ORR potential that we observed is comparable to the performance of the best-known bimetallic catalysts.
