Interfacial studies of the HOR/HER mechanism on Pt in alkaline electrolytes
Date
2024
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Publisher
University of Delaware
Abstract
A global hydrogen–based economy using hydrogen fuel cells and electrolyzers in tandem with renewables has the potential to transition our society toward a net-zero CO2 emissions goal. ☐ Current state–of–the–art acid–based electrolyzers and fuel cells are, however, impractically expensive due to their high precious metal requirements, leading many researchers to develop alkaline based alternatives. The typically fast hydrogen electrocatalysis in acidic environment becomes very slow in alkaline media, thus also requiring high precious metal loadings and making these devices economically infeasible. To facilitate better catalyst design, the underlying parameters influencing the reaction mechanism must be understood. ☐ In this thesis, we systematically analyze the leading hypotheses proposed to explain the ~100 times electrocatalytic activity decrease in alkaline media using electrochemical and spectroscopic techniques. Using crown ethers, we demonstrate that alkali metal cations specifically adsorb on platinum in base, but do not influence reactivity through modulation of adsorbed hydroxide’s binding energy. Instead, adsorbed crown ethers and benzyl tri alkyl ammonium cations enable a higher degree of hydrogen bonding amongst interfacial water and allow for facile proton and hydroxide shuttling between the surface and the liquid bulk. Establishing water structural entropy as the alkaline hydrogen electrocatalysis activity descriptor enables rational catalyst design to lower fuel–cell and electrolyzer overpotentials increasing their economic viability.
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Keywords
Electrocatalysis, Electrochemistry, Hydrogen oxidation, Platinum, Reaction mechanism