The highly conjugated linkage between a molecular moiety and an electrode often involves a specific type of functional group (e.g., o-quinone) that requires pretreating the electrode and leads to a low catalyst loading. Immobilizing metalloporphyrins onto a conductive oxide support via grafting illustrates yet another possibility towards catalytic activity enhancement. Electrodes composed of nanostructured indium tin oxide (nanoITO) were prepared either by direct grafting of a cobalt porphyrin complex forming CoP|nanoITO or grafting a layer of poly(vinylpyrindine) followed by coordination to the cobalt center through the pyridine group forming CoTPP|PVP|nanoITO (Figure ). With ITO as the supporting electrode, the metal center was responsible for the redox process. A cyclic voltammetry study of CoP|nanoITO electrodes displayed two one-electron redox processes corresponding to Co III/II and Co II/I at a half potential E1/2 of 0.15 and -1.19 V vs. Fc + /Fc. In contrast, under the same conditions, redox events at -0.2 and -1.34 V vs. Fc + /Fc were observed for CoTPP|PVP|nanoITO. These redox potential shifts represent a direct manipulation of the electrochemical property of the hybridized electrocatalyst by changing the interaction between the electrode and the molecular species. However, controlling the number of cobalt complexes that can be coordinated to the polymer chain remains challenging. Possible non-covalent interactions of the porphyrin ligand with the electrode surface, as well as metal complexes coordinated to the pyridine unit that is too far away from the electrode, may complicate the system. Covalent immobilization via diazonium grafting is also widely applied in preparing immobilized molecular electrocatalysts. Covalently grafted Ir complexes onto carbon electrodes achieved a turnover frequency of up to 3.3 s -1 and a turnover number of 644 during the first hour of electrochemical water oxidation reaction (Figure ). However, there was a minor loss of carbon material on the electrode surface, decreasing the catalytic activity. Nevertheless, enhanced activity was observed compared to the molecular analogue. Encouraged by the incredible behavior of the grafted carbon-based electrode in water oxidation reactions, various metal complexes including Mn porphyrin were investigated applying the same immobilization strategy. Both covalently and non-covalently immobilized Mn porphyrin complexes were employed in water oxidation and oxygen reduction reactions. Covalent ligation of the Mn complex onto a carbon electrode through electroreduction of a porphyrin diazonium salt followed by metalation and electrodeposition yielded an electrochemically active catalyst with a controllable amount of active sites. The immobilized catalyst reached an overall catalytic current for the oxygen reduction reaction 2.4 times higher than that of the non-covalently anchored catalyst. The proposed explanation for the improvement was due to the shorter average Mn-Mn distance, which enabled the simultaneous participation of two metals (Figure ). Note that changing the electrodeposition time, therefore changing the concentration of Mn active sites on the electrode surface, allowed two metal centers to participate in the 4-electron process.