Research Progress in Cucurbit[n]uril-Based Metal Nanomaterials for Electrocatalytic Applications

Metal nanomaterials have exhibited excellent performance in electrocatalytic applications, but they still face the problems of poor stability and limited regulation strategies. It is an efficient strategy for greatly enhanced catalytic activity and stability by introducing a second component. In this review, we provide the sketch for the combination of metal nanomaterials and cucurbit[n]urils (CB[n]s) in electrocatalytic applications. CB[n]s are a series of macrocycles with rigid structure, high stability, and function groups for coordinating with metal sites, which make them promising to stabilize and modulate the metal nanomaterials for ideal performance. The discussion classifies the roles of CB[n]s, involving CB[n]s as protecting agents, CB[n]-based supramolecular self-assemblies and CB[n]s as the precursor for the preparation of N-doped holy carbon matrix. Various metal nanocatalysts including metal (Pt, Ir, Pd, Ru, Au) nanoparticles, metal (Fe, Co, Ni) single-atoms, and transition metal carbides (TMCs) have been integrated with CB[n] orCB [n]-derived carbon matrix. These nanomaterials show superior activity and stability in multiple electrocatalytic reactions, including oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO2RR), methanol oxidation reaction (MOR), and ethanol oxidation reaction (EOR). Furthermore, a few metal-CB[n] composites can become bifunctional catalysts applied in the overall water splitting and fuel cell. It is surprising that the activity of CB[n]-based nanocatalysts is comparable with that of commercial catalyst, and the stability is even better. The experimental analysis together with the density functional theory (DFT) calculations verifies that the improvement can be attributed to the interaction between the metal nanocrystal and CB[n]s as well as the characteristic stability of CB[n]s. Finally, we talk about the challenges and opportunities for the cucurbit[n]uril-based electrocatalysis. This review provides an impressive strategy to obtain welldefined metal nanomaterials constructed with CB[n]s with enhanced performance, and expects that such a strategy will develop more efficient catalysts for a broader range of electro-applications.