Demonstrating Electrochemical CO$_2$ Capture on Redox-Active Metal-Organic Frameworks

TL;DR

This paper introduces a novel redox-active metal-organic framework, Cu3(HHTP)2, capable of reversible electrochemical CO2 capture in aqueous solutions, offering a new approach to carbon capture technology.

Contribution

It demonstrates for the first time that a MOF can switch its CO2 capture ability electrochemically in aqueous electrolytes, expanding materials options for electrosorption.

Findings

Cu3(HHTP)2 can reversibly capture and release CO2.

The material has a CO2 capacity of 2 mmol g$^{-1}$.

Electrosorption is facilitated by redox-active copper and aromatic ligands.

Abstract

Addressing climate change calls for action to control CO$_2$ pollution. Direct air and ocean capture offer a solution to this challenge. Making carbon capture competitive with alternatives, such as forestation and mineralisation, requires fundamentally novel approaches and ideas. One such approach is electrosorption, which is currently limited by the availability of suitable electrosorbents. In this work, we introduce a metal-organic copper-2,3,6,7,10,11-hexahydroxytriphenylene (Cu$_3$(HHTP)$_2$) metal-organic framework (MOF) that can act as electrosorbent for CO$_2$ capture, thereby expanding the palette of materials that can be used for this process. Cu$_3$(HHTP)$_2$ is the first MOF to switch its ability to capture and release CO$_2$ in aqueous electrolytes. By using cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS), galvanostatic charge-discharge (GCD) analysis, and differential electrochemical mass spectrometry (DEMS), we demonstrate reversible CO$_2$ electrosorption. Based on density functional theory (DFT) calculations, we provide atomistic insights into the mechanism of electrosorption and conclude that efficient CO$_2$ capture is facilitated by a combination of redox-active copper atom and aromatic HHTP ligand within Cu3(HHTP)2. By showcasing the applicability of Cu$_3$(HHTP)$_2$ -- with a CO$_2$ capacity of 2 mmol g$^{-1}$ and an adsorption enthalpy of -20 kJ mol$^{-1}$ - this study encourages further exploration of conductive redox-active MOFs in the search for superior CO$_2$ electrosorbents.