We build on the success of phosphoric acid as a fuel cell electrolyte, by designing a variant of the molecular acid that provides increased temperature range without sacrifice of high temperature conductivity or open circuit voltage. This is achieved by introduction of a hybrid component, based on silicon coordination of phosphate groups, which prevents decomposition or water loss to 250 degrees C, while enhancing free proton motion. We report conductivity studies to 285 degrees C and full H-2/O(2)cell polarization curves to 226 degrees C with careful monitoring of fuel consumption. The current efficiency we report (current density per unit of fuel supplied per sec) is as high as the highest on record. A power density of 184 mW cm(-2) is achieved at 226 degrees C with hydrogen flow rate of 4.1 ml min(-1). (C) 2013 Elsevier B.V. All rights reserved.