RESUMO
Using powder X-ray diffraction and AC impedance spectroscopy, we have found that the superprotonic CsH2PO4 (CDP) phase is stable at T = 250 °C when sealed in different volumes (15 mL and 50 mL) of dry air or inert gasses. Under these conditions, CDP's proton conductivity stays constant at 2.5 × 10-2 S·cm-1 for at least 10 h. On the other hand, removing the gas from the chamber leads to a sharp, two-order-of-magnitude drop in the proton conductivity. Our data show no evidence of a self-generated water vapor atmosphere in the chamber, and the gas pressure at T = 250 °C is several orders of magnitude below the pressures previously used to stabilize CDP's superprotonic phase. These results demonstrate that hermetically sealing CDP in small gas-filled volumes represents a new method to stabilize the superprotonic phase, which opens new paths for large-scale applications of phosphate-based solid acids as fuel cell electrolytes.
RESUMO
Herein, we report a crystalline CoTcPP-based [TcPP = the anion of meso-tetra(4-carboxyphenyl)porphyrin] polymeric system, 1, as a hydrogen evolution reaction (HER) electrocatalyst in acidic aqueous media. The material was characterized by powder X-ray diffraction (p-XRD), Fourier transform infrared (FT-IR) spectroscopy, and energy dispersive X-ray (EDX) analysis and its morphology was probed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Polymer 1 shows a surface area of 441.74 m3 g-1, while the discrete CoTcPP molecule (2) shows a surface area of 3.44 m3 g-1. The HER catalytic performance was evaluated by means of linear sweep voltammetry in the presence of 0.5 M H2SO4 aqueous solution. To achieve 10 mA cm-2 cathodic current density, 1 and 2 respectively require an overpotential of 0.475 V and 0.666 V, providing strong evidence that the extended network of cobalt-based porphyrin leads to enhanced HER efficiency. The polymer also shows great tolerance for HER electrolysis in the presence of an acid remaining active over 10 hours.