Rapidly increasing atmospheric CO2 concentrations threaten human society, the natural environment, and the synergy between the two. In order to ameliorate the CO2 problem, carbon capture and conversion techniques have been proposed. Metal–organic framework (MOF)-based materials, a relatively new class of porous materials with unique structural features, high surface areas, chemical tunability and stability, have been extensively studied with respect to their applicability to such techniques. Recently, it has become apparent that the CO2 capture capabilities of MOF-based materials significantly boost their potential toward CO2 conversion. Furthermore, MOF-based materials’ well-defined structures greatly facilitate the understanding of structure–property relationships and their roles in CO2 capture and conversion. In this review, we provide a comprehensive account of significant progress in the design and synthesis of MOF-based materials, including MOFs, MOF composites and MOF derivatives, and their application to carbon capture and conversion. Special emphases on the relationships between CO2 capture capacities of MOF-based materials and their catalytic CO2 conversion performances are discussed.

Carbon capture and conversion using metal–organic frameworks and MOF-based materials

Photocatalysts and Photoelectrodes James L. White,† Maor F. Baruch,† James E. Pander III,† Yuan Hu,† Ivy C. Fortmeyer,† James Eujin Park,† Tao Zhang,† Kuo Liao,† Jing Gu,‡ Yong Yan,‡ Travis W. Shaw,† Esta Abelev,† and Andrew B. Bocarsly*,† †Department of Chemistry, Princeton University, Princeton, New Jersey 08544, United States ‡Chemical and Materials Science Center, National Renewable Energy Laboratory, Golden, Colorado 80401, United States

Light-Driven Heterogeneous Reduction of Carbon Dioxide: Photocatalysts and Photoelectrodes

Metal-organic framework (MOF) nanoparticles, also called porous coordination polymers, are a major part of nanomaterials science, and their role in catalysis is becoming central. The extraordinary variability and richness of their structures afford engineering synergies between the metal nodes, functional linkers, encapsulated substrates, or nanoparticles for multiple and selective heterogeneous interactions and activations in these MOF-based nanocatalysts. Pyrolysis of MOF-nanoparticle composites forms highly porous N- or P-doped graphitized MOF-derived nanomaterials that are increasingly used as efficient catalysts especially in electro- and photocatalysis. This review first briefly summarizes this background of MOF nanoparticle catalysis and then comprehensively reviews the fast-growing literature reported during the last years. The major parts are catalysis of organic and molecular reactions, electrocatalysis, photocatalysis, and views of prospects. Major challenges of our society are addressed using these well-defined heterogeneous catalysts in the fields of synthesis, energy, and environment. In spite of the many achievements, enormous progress is still necessary to improve our understanding of the processes involved beyond the proof-of-concept, particularly for selective methane oxidation, hydrogen production, water splitting, CO2 reduction to methanol, nitrogen fixation, and water depollution.

State of the Art and Prospects in Metal-Organic Framework (MOF)-Based and MOF-Derived Nanocatalysis.

Metal-organic frameworks (MOFs), also called porous coordination polymers, represent a class of crystalline porous materials built from organic linkers and metal ions/clusters. The unique features of MOFs, including structural diversity and tailorability as well as high surface area, etc., enable them to be a highly versatile platform for potential applications in many fields. Herein, an overview of recent developments achieved in MOF catalysis, including heterogeneous catalysis, photocatalysis, and eletrocatalysis over MOFs and MOF-based materials, is provided. The active sites involved in the catalysts are particularly emphasized. The challenges, future trends, and prospects associated with MOFs and their related materials for catalysis are also discussed.

Metal-Organic Frameworks as Platforms for Catalytic Applications.

This Review details the structural and chemical features of state-of-the-art metal–organic frameworks for their application in the entire carbon cycle of capturing, purifying and transforming CO 2 into valuable products.

The chemistry of metal–organic frameworks for CO 2 capture, regeneration and conversion

We synthesized a copper rubeanate metal organic framework (CR-MOF) which has the potential to improve the catalytic activity of electrochemical reduction of CO2 due to its characteristics of electronic conductivity, proton conductivity, dispersed reaction sites, and nanopores. Synthesized CR-MOF particles were dropped on carbon paper (CP) to form a working electrode. The onset potential for CO2 reduction of a CR-MOF electrode was about 0.2 V more positive than that observed on a Cu metal electrode in an aqueous electrolyte solution. Our analysis of the reduction products during potentiostatic electrolysis showed formic acid (HCOOH) to be virtually the only CO2 reduction product on a CR-MOF electrode, whereas a Cu metal electrode generates a range of products. The quantity of products from the CR-MOF electrode was markedly greater (13-fold at −1.2 V vs. SHE) than that of a Cu metal electrode. Its stability was also confirmed.

https://iopscience.iop.org/article/10.1149/2.001204eel/pdf

Electrochemical Reduction of Carbon Dioxide Using a Copper Rubeanate Metal Organic Framework

CO2 reduction with water and light illumination is realized using a gallium nitride (GaN) photoelectrode in which excited electrons induce CO2 conversion at the counter electrode. For the counter electrode, a copper (Cu) plate was chosen. The low affinity and wide gap of the nitride semiconductor enable us to create an electron–hole pair which has a sufficient energy for both CO2 reduction and water oxidation, in spite of the fact that a high energy for CO2 reduction is required. Within this system, the generation of formic acid (HCOOH) with 3% Faradic efficiency was confirmed by light illumination alone.

https://iopscience.iop.org/article/10.1143/APEX.4.117101/pdf

Photo-induced CO 2 Reduction with GaN Electrode in Aqueous System

Understanding the oxygen evolution reaction (OER) is crucial for improving the performance of water electrolysis. Copper delafossite oxides (CuBO2, B = transition metal) were investigated for their potential as OER catalysts using density functional theory (DFT) calculations. To identify an appropriate descriptor for OER activity, we examined the relationships between the calculated eg or t2g occupancy of the B site and the experimentally determined OER activity. The calculated t2g occupancy was found to be approximately linearly related to OER activity. We therefore propose that t2g occupancy can be employed as an appropriate descriptor of the OER activity of delafossite oxide catalysts. The d-electron occupancy of active sites, estimated using theoretical calculations, can be used to search efficiently for transition metal oxide catalysts with high OER activity.

Calculated Descriptors of Catalytic Activity for Water Electrolysis Anode: Application to Delafossite Oxides

Light illumination of a gallium nitride photoelectrode creates separate electron-hole pairs that drive water oxidation and CO2 reduction reactions. Here, we show enhanced photocurrent in an AlGaN/GaN device that consists of an unintentionally doped (uid-) AlGaN photoabsorption layer and an n+-GaN electrical-conduction layer. The production rate of formic acid by CO2 conversion in the uid-AlGaN/n+-GaN photoelectrode is about double that in the uid-GaN/n+-GaN device. This improvement is most likely due to the effect of internal bias in the uid-AlGaN layer generated by the polarization effect, which improves electron-hole separation.

Reiko Hinogami

Papers

Electrochemical Reduction of Carbon Dioxide Using a Copper Rubeanate Metal Organic Framework

Photo-induced CO 2 Reduction with GaN Electrode in Aqueous System

Calculated Descriptors of Catalytic Activity for Water Electrolysis Anode: Application to Delafossite Oxides

Enhanced CO2 reduction capability in an AlGaN/GaN photoelectrode

Active copper delafossite anode for oxygen evolution reaction