Alternating misfit layered transition/alkaline earth metal chalcogenide Ca₃Co₄O₉ as a new class of chalcogenide materials for hydrogen evolution

Layered misfit chalcogenide structures have garnered much attention and prestige in several applications such as thermoelectric materials and high-temperature superconductors. However, its potentials for important electrochemical applications such as hydrogen evolution and oxygen reduction reactions have not been systematically studied. Till date, such applications have mainly applied precious metal and oxides with perovskite- or spinel-based structures. In this work, we synthesized a misfit layered mixed oxide in the form of Ca₃Co₄O₉ and investigated its structural, morphological, and electrochemical properties. The misfit layered Ca₃Co₄O₉ has promising capabilities as electrocatalyst for hydrogen evolution and oxygen reduction processes. A Tafel slope of 87 mV/decade for hydrogen evolution reaction was achieved by Ca ₃Co₄O₉, while the overpotential for oxygen reduction reaction was lowered up to 38 mV in comparison to glassy carbon. Moreover, a comparably higher heterogeneous electron transfer rate of 3.76 × 10^-4 cm s^-1 was achieved for Ca₃Co ₄O₉ compared to 3.11 × 10^-4 cm s ^-1 for glassy carbon. The affordability and electrocatalytic properties have endowed Ca₃Co₄O₉ as a potential replacement for precious metal in electrocatalysis and electrochemical sensing applications.