Recently, N-heterocyclic carbenes (NHCs) were also found to bound firmly with metal electrodes, and displayed the potential to form length-adjustable polymer brushes binding with active species (Figure ). In the recent decade, manifold immobilization strategies were developed for metal surfaces in addition to gold. Chang and coworkers directly anchored supramolecular cages of cobalt porphyrins on a copper electrode surface by using the strong interaction between thiol groups and copper (Figure ). However, it is worth noting that metal surfaces tend to participate in redox reactions which cannot be fully disentangled from the activity of the immobilized complexes. In light of the growing economic concerns, precious metal surfaces are deprioritized for surface functionalization in our perspective. Metal oxides are a promising platform for immobilization because of their accessibility, thermodynamic stability, and potential to be prepared in various nanometer-sized structures. In addition to the abundant anchoring units on the surface, such as hydroxyl groups, metal oxides display highly tunable optical and electrical characteristics (e.g., transparent and electrically conductive indium tin oxide, fluorine-doped tin oxide, and semiconductive titanium oxide). Like carbon-based electrodes, metal oxides can be used for covalent or non-covalent immobilization. For example, anchoring sites on metal oxides surface, including oxyacids (e.g., carboxylic acids, phosphonic acids, and hydroxamic acid) and silatranes, covalently bind to metal oxide surfaces in various ways (Figure ). Except for hydroxamic acids, which exhibit mono-chelating binding mode, the most popular binding mode for the abovementioned oxyacids and silatranes is bridging bidentate. These tendencies of binding mode could be analyzed by the existence or disappearance of infrared active bonds after being bound to the metal oxide surface (e.g., C=O stretching in carboxylic acids disappeared after the anchoring group followed bridging bidentate binding modes on the metal oxide surface).