Calixarene-Functionalized Stable Bismuth Oxygen Clusters for Specific CO2‑to-HCOOH Electroreduction

Designing and synthesizing well-defined crystalline catalysts for long-term electrocatalytic conversion of CO2 to specific products remain a great challenge. In this work, two very stable crystalline bismuth oxygen clusters functionalized by hydrophobic p-tert-butylthiacalix[4]arene ligand, Bi3 and Bi14, were constructed and treated as catalysts for efficient electrochemical CO2 reduction. Sandwich-type Bi3 with synergistic bi-bismuth exhibits a remarkable performance for CO2-to-HCOOH conversion with a faradaic efficiency (FEHCOOH) of 96.47% at −1.3 V (vs reversible hydrogen electrode) and durability over 27.5 h, while rodlike Bi14 with a monobismuth active site reached a maximum FEHCOOH of 92.76% at −1.2 V with durability over 23.9 h. Density functional theory calculation proves that adjacent double active bismuth atoms in Bi3 are more beneficial to stabilize the *OCHO intermediate and then promote the electrocatalytic reduction of CO2 to HCOOH than Bi14 with a single active site. This work represents the report of stable crystalline bismuth-oxo cluster catalysts for specific electrocatalytic CO2 reduction conversion.