Microstructural Effects on Intermediate Temperature Proton Conduction in an Oxalate-based Coordination Polymer

Abstract

Microstructure control of the CP proton conductor {[((CH₃)₂NH₂)₃SO₄]₂[Zn₂(C₂O₄)₃]}_n (DSZO) offers improved powder processing capabilities and formation of dense electrolyte pellets. Particles of different sizes were obtained through varying reaction time (60 or 15 μm), or by ball milling (0.2 μm). Analyses of the impedance, modulus, and permittivity spectra were used to elucidate the grain boundary and bulk contributions as a function of grain size. The small-grained (0.2 μm) sample has higher proton conductivity than the larger-grained samples at elevated temperatures (100–160 °C), and the different microstructures are found to have variations in response to mild humidification (0.5% RH), where the small-grained microstructure leads to numerous hydrated grain boundaries, achieving two orders of magnitude higher conductivity. Moreover, sintering behaviour is observed, particularly in the smaller grained samples (15 and 0.2 μm).