Electrocatalytic activity of MnxOy-derived metal-organic frameworks for lithium-ion batteries, hydrogen evolution reaction and oxygen evolution reaction

The electrocatalytic activity of MnxOy materials derived from the metal-organic framework (Mn-BTC) was investigated in dry (for lithium-ion batteries (LIBs)) and wet (for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER)) conditions while observing the phase transformation from annealing Mn-BTC in the air. As a result, the partial α-MnO2, Mn3O4, and Mn2O3 phases were formed at 300, 500, and 700 °C, respectively. The electrocatalytic activity of MnxOy materials follows the order (Mn3O4 > Mn2O3 > α-MnO2 > Mn-BTC) in both dry and wet conditions. For instance, Mn3O4 electrodes delivered an initial discharge/charge capacity of 1302/815 mAh g−1 with an initial Coulombic efficiency of 62.6% when used as anodes for LIBs. They also exhibited a lower Tafel slope of 116 and 54 mV dec−1 when applied to HER and OER, respectively. The structural analysis showed that the best electrocatalytic activity of Mn3O4 samples originated from the spinel Mn3O4 structure with Mn2/Mn3+ ions occupying the tetrahedral and octahedral sites, high electrical conductivity and small grain size. This study provides insights into the role of physicochemical properties in controlling MnxOy phases from Mn-BTC materials via the annealing process towards applications as potential electrode materials for LIBs, HER, and OER.