Perovskite-type catalysts prepared by nanocasting: effect of metal silicates on the electrocatalytic activity toward oxygen evolution and reduction reactions

La0.6Sr0.4Fe0.6Mn0.4O3-? (LSFM) perovskite-type catalysts were prepared by a nanocasting route based on solution combustion synthesis, called the soft-hard templating (SHT) approach. Three silica hard templates with different textural properties were used to increase the specific surface area of the perovskites, and hence to improve their electrochemical activity for both oxygen evolution and reduction reactions. Careful structural and physicochemical characterization revealed that the materials are composites formed by crystalline LSFM perovskite and amorphous metal silicates, even after the etching procedure. Both the composites' specific surface area and the fraction of silicates are proportional to the silicas pore volume. Interestingly, the LSFM perovskite obtained by SHT has lower cell volumes than the parent oxide prepared without a silica template. The electrochemical characterization revealed the contrasting effects of the metal silicates on the performances of the electrodes. The LSFM-SHT-based electrodes have higher double-layer capacitance and higher current for oxygen evolution than those prepared with the parent LSFM. Furthermore, the LSFM-SHT-based electrodes show a preferential 4-electron pathway during the oxygen reduction reaction, if the amount of amorphous silicates is low (Si wt % < 3.5 wt %). However, the silicates also shift the onset potential of both oxygen evolution and reduction reactions to more positive and negative potential values, respectively, thus delaying the two reactions.