Fluorocarbon Film on an Electrocatalyst as a Confined Proton Exchange Membrane—A Potentially Scalable Approach

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A scalable approach for ultrathin ion exchange films having high selectivity and permeance is highly sought after. Here, we report a fluorocarbon (CF) ink based coating for selective proton transport while blocking competing ions (SO42–), methanol, and gases such as O2 and CO. This proton exchange membrane (PEM) further brings alterations to the innate electrocatalytic hydrogen evolution reaction (HER) activity of metal catalysts, shedding light on the possible proton confinement effects, in line with the phenomenological predictions. The effect enhances the HER activity of Pt, Ni, Fe, Pd, Mo, and W but suppresses that in Au and Cu. The CF PEM restricts water permeation, too, demonstrating a drastic transition in the HER rate determining step from Tafel to Volmer by a pH of ∼2. Hence, the CF on catalysts brings a plethora of possibilities in electrocatalysis, namely, seawater electrolysis, HER without removing dissolved oxygen, Pt protection in direct methanol fuel cells, etc., marking this finding as a significant advancement with broad potential applications.