cs5b01779_si_001.pdf (1.13 MB)
Water as a Promoter and Catalyst for Dioxygen Electrochemistry in Aqueous and Organic Media
journal contribution
posted on 2015-12-17, 10:33 authored by Jakub Staszak-Jirkovský, Ram Subbaraman, Dusan Strmcnik, Katharine
L. Harrison, Charles E. Diesendruck, Rajeev Assary, Otakar Frank, Lukáš Kobr, Gustav K. H. Wiberg, Bostjan Genorio, Justin G. Connell, Pietro P. Lopes, Vojislav
R. Stamenkovic, Larry Curtiss, Jeffrey
S. Moore, Kevin R. Zavadil, Nenad M. MarkovicWater and oxygen electrochemistry
lies at the heart of interfacial
processes controlling energy transformations in fuel cells, electrolyzers,
and batteries. Here, by comparing results for the ORR obtained in
alkaline aqueous media to those obtained in ultradry organic electrolytes
with known amounts of H2O added intentionally, we propose
a new rationale in which water itself plays an important role in determining
the reaction kinetics. This effect derives from the formation of HOad···H2O (aqueous solutions) and
LiO2···H2O (organic solvents)
complexes that place water in a configurationally favorable position
for proton transfer to weakly adsorbed intermediates. We also find
that, even at low concentrations (<10 ppm), water acts simultaneously
as a promoter and as a catalyst in the production
of Li2O2, regenerating itself through a sequence
of steps that include the formation and recombination of H+ and OH–. We conclude that, although the binding
energy between metal surfaces and oxygen intermediates is an important
descriptor in electrocatalysis, understanding the role of water as
a proton-donor reactant may explain many anomalous features in electrocatalysis
at metal–liquid interfaces.