**4. Detailed chemistry and electrochemistry of MnO2 and Co3O4**

The oxides of manganese and cobalt still remain prominent alternatives for precious materials and have been extensively investigated in many growing areas such as lithium-ion batteries, supercapacitors and electrochemical sensors, as well as in electrocatalysis, due to their appreciable unique properties, affordability and environmental friendliness. So, before moving to recent explorations of these materials, the detailed properties and their influence in electrocatalysis have been discussed here more elaborately one by one.
