A porous electrochemical electrode is made up of a solid cellular material provided in the form of a semi-graphitized carbon monolith comprising a hierarchized porous network free of mesopores and including macropores with a mean dimension dA of 1 μm to 100 μm, and micropores with a mean dimension dI of 0.5 nm to 2 nm, said macropores and micropores being interconnected. In said electrode, the macropores contain at least one electroactive species in direct contact with the semi-graphitized carbon that makes up the surface of the macropores. The invention also relates to a method for preparing such an electrode as well as to the use thereof as a biosensor or for manufacturing a biopile.