Gelation of a metal oxide cluster for a proton exchange membrane operated under low humidity

Commercial proton exchange membranes (PEMs) have high requirements for environmental humidity, which significantly narrows the applications of PEM-assembled fuel cells and raises the costs of humidity maintenance. Herein, polyvinyl alcohol and a nanosized metal oxide cluster (MOC) are complexed with glycerol and boric acid for the fabrication of hybrid hydrogels. The formation of dynamic reversible bonds and multiple supramolecular interactions among the structural units contributes to the simultaneous achievement of appreciable mechanical strength and (re)processability. The as-formed enriched hydrogen bonding networks provide highways for fast proton conduction, while the solvent molecules can be tightly trapped by the gels' nano-confined cavities. The appreciable proton conductivity and excellent water retention capacity project the application of the gel at low humidity. EIS analysis demonstrates that the proton conductivity of the resultant gel can reach as high as 4.7 x 10-4 S cm-1 at 30% relative humidity. Upon further assembly into a single fuel cell, the working plots of the as-assembled devices show satisfactory maximal power density of 141 mW cm-2 under dry gas conditions. Our design protocol opens up a new avenue for the fabrication of cluster-based gel PEMs applicable for use at low humidity. Metal oxide clusters are complexed with polyvinyl alcohol and glycerol into gel electrolytes, which serve as proton exchange membrane in fuel cell with maximum power density of 141 mW cm-2 under dry gas condition.