The role of the protein–water interface in dictating proton conduction across protein-based biopolymers

Proton conducting polymers have become central in recent years, and especially for energy related applications. As such, unraveling their proton transport mechanism is of prime importance, specifically the different contribution of proton transport across bulk water inside the polymer vs. the transport at the interface between the polymer and water. In recent years, proton conducting biopolymers have been proven to be a green and sustainable alternative to traditional polymers. Unlike traditional synthetic polymers, the protein-based biopolymers that we use here can uptake a significant amount of water reaching 150 wt%, which might suggest a large contribution of bulk water proton transport vs. the protein–water interface one. We directly tackle the latter question and decipher the contribution of the protein–water interface in mediating proton conduction across our electrospun biopolymer by introducing two alternative experimental approaches. The first is to follow proton conduction across a highly aligned mat in parallel vs. perpendicular to the fiber direction, while the second is to measure proton conduction across a 'completely dry' network of the protein fibers. We conclude that although the protein-based mat contains a substantial amount of water, proton transport is mediated along the protein–water interface.