A cathode can include: an electrode substrate; a porphyrin precursor attached to the substrate; and an enzyme coupled to the electrode substrate to be associated with the porphyrin precursor, the enzyme reduces oxygen. The cathode can include a conductive material associated with the porphyrin precursor and/or the enzyme. The cathode can include 1-pyrenebutanoic acid, succinimidyl ester (PBSE) associated with the porphyrin precursor and/or the enzyme and/or the conductive material. The cathode can include 2,5-dimethyl-1-phenyl-1H-pyrrole-3-carbaldehyde (DMY-Carb) associated with the 1-pyrenebutanoic acid, succinimidyl ester (PBSE) and/or the porphyrin precursor and/or the enzyme and/or the conductive material. The porphyrin precursor is attached to the substrate through covalent coupling. In some aspects, substrate is linked to the porphyrin precursor, the porphyrin precursor is linked to the conductive material, the conductive material is linked to the PBSE, the PBSE is linked to the DMY-carb, and the DMY-carb is linked to the enzyme.