Ligand substitution could exert extra through-space stabilization to key intermediates and provide coordination sites to the electrode to create strong interaction depending on the immobilization method. Meanwhile, substituents exert inductive effect to the electronic structure of the catalytically active metal center. Furthermore, bulky substituents may decrease the possibility of aggregation but the density of the catalyst coverage at the same time. It is worth noting that the optimal ligand design for the organometallic catalyst may not perform the best in the immobilized form, as demonstrated in the iron porphyrin complex bearing mesityl substituents. The underlined importance and complexity of ligand substitution effects should be considered when designing an immobilized molecular catalyst for optimal performance.