Electro- and Solar-Driven Fuel Synthesis with First Row Transition Metal Complexes

Abstract

The synthesis of renewable fuels from abundant water or the greenhouse gas CO 2 is a major step toward creating sustainable and scalable energy storage technologies. In the last few decades, much attention has focused on the development of nonprecious metal-based catalysts and, in more recent years, their integration in solid-state support materials and devices that operate in water. This review surveys the literature on 3d metal-based molecular catalysts and focuses on their immobilization on heterogeneous solid-state supports for electro-, photo-, and photoelectrocatalytic synthesis of fuels in aqueous media. The first sections highlight benchmark homogeneous systems using proton and CO 2 reducing 3d transition metal catalysts as well as commonly employed methods for catalyst immobilization, including a discussion of supporting materials and anchoring groups. The subsequent sections elaborate on productive associations between molecular catalysts and a wide range of substrates based on carbon, quantum dots, metal oxide surfaces, and semiconductors. The molecule–material hybrid systems are organized as “dark” cathodes, colloidal photocatalysts, and photocathodes, and their figures of merit are discussed alongside system stability and catalyst integrity. The final section extends the scope of this review to prospects and challenges in targeting catalysis beyond “classical” H 2 evolution and CO 2 reduction to C 1 products, by summarizing cases for higher-value products from N 2 reduction, C x >1 products from CO 2 utilization, and other reductive organic transformations.

Iron Porphyrin Allows Fast and Selective Electrocatalytic Conversion of CO2 to CO in a Flow Cell

“…Therefore, new approaches are needed to develop electrolyzers operating at industrially relevant scales while fulfilling customer needs and requirements. Regarding the catalysts employed, molecular complexes have been widely investigated for the carbon dioxide reduction reaction (CO 2 RR) due to the possibility of fine tuning the ligand structure (steric and electronic effects, as well as second coordination sphere effects) . Earth abundant metal‐based catalysts have been shown to efficiently catalyze the production of CO and formate in organic solvents and in water, even if examples in pure aqueous solutions are less numerous.…”

Comprehensive review and future perspectives on the photocatalytic hydrogen production

“…Hydrogen production catalysts based on solid‐state materials are usually stable but exhibit low selectivity and high sensitivity to poisoning. By contrast, as their chemical properties can be tailored through judicious choices of metal and ligands, molecular catalysts based on transition metal complexes enjoy good selectivity and tolerance to varied experimental conditions . Over the last decades, the design of molecular catalysts has been inspired by metalloenzymes, which generally possess first row transition metals in their active sites.…”

“…Practical use of molecular catalysts hence will be greatly facilitated if they are able to utilize H 2 O as proton source or at least tolerate the presence of H 2 O . The various strategies developed for immobilization of molecular catalysts on solid‐state supports represent good solutions to this issue, while also helping the implementation and recycling of the catalytic system . Anchoring to metal oxide semiconductor can be achieved by introducing carboxylate, phosphonate or silane groups in the ligands of the transition metal complexes.…”

A Hybrid Artificial Photocatalysis System Splits Atmospheric Water for Simultaneous Dehumidification and Power Generation

“…Research on artificial photocatalysis has made a huge progress in recent times and the great quest nowadays is the production of clean chemical fuels from photo‐electrochemical (PEC) reactions . In most cases, the photocatalytic cells require aqueous solution condition (e.g., sea or waste water splitting), posing difficulties for mass production due to the essential bulk liquid. Earth's atmosphere contains an amazing 1.29 × 10 16 kg of water, a level that is almost unchanged attributed to oceans and plants.…”