Splitting CO ₂ into CO and O ₂ by a single catalyst

Abstract

The metal complex ½ðtpyÞðMebim-pyÞRu II ðSÞ 2þ (tpy ¼ 2,2 0 : 6 0 ,2 0 0 -terpyridine; Mebim-py ¼ 3-methyl-1-pyridylbenzimidazol-2-ylidene; S ¼ solvent) is a robust, reactive electrocatalyst toward both water oxidation to oxygen and carbon dioxide reduction to carbon monoxide. Here we describe its use as a single electrocatalyst for CO 2 splitting, CO 2 → CO þ 1∕2 O 2 , in a two-compartment electrochemical cell.artificial photosynthesis | polypyridyl Ru complexes | proton coupled electron transfer | single-site catalysis | solar fuels R ising energy prices, diminishing reserves of petroleum, and environmental concerns are driving new thinking about our energy future. Given its availability, with approximately 10,000 times the daily energy input required to meet current energy consumption, solar energy could be the ultimate answer. However, solar energy is diffuse, spread over the earth's surface, and requires vast collection areas for large-scale applications (1). A more difficult challenge is the intermittency of the sun as an energy source. Meeting the challenge of providing power at night will require energy storage on massive scales at levels exceeding the ability of existing or foreseeable energy storage technologies (2, 3). The only realistic alternative is energy storage in chemical bonds and the increasingly popular concept of "solar fuels." Solar fuels mimic natural photosynthesis in using solar energy and artificial photosynthesis to convert readily available sources, water and carbon dioxide, into highenergy fuels. Target reactions include water splitting into hydrogen and oxygen and reduction of carbon dioxide to carbon monoxide, other oxygenates, or hydrocarbons (Eqs. 1-3), as follows:Carrying out these reactions presents a major challenge in chemical reactivity given their multiphoton, multielectron, multiatom character. It is reassuring that similar hurdles have been overcome in natural photosynthesis, in which light-driven reduction of CO 2 to carbohydrates by water occurs (Eq. 4). However, photosynthesis in green plants took 2-3 billion years to evolve and utilizes a complex architecture that utilizes thousands and thousands of atoms and multiple integrated assemblies (4, 5).A simplifying factor, suggesting a mechanistic approach, comes with recognition that the target energy storage reactions can be split into constituent "half reactions" which are shown for CO 2 splitting in Eqs. 5 and 6. Photosynthesis in green plants occurs in the thylakoid membrane and uses physically separated molecular assemblies for light-driven water oxidation (Photosystem II) and CO 2 reduction (Photosystem I and the Calvin cycle) (6, 7). Electron/proton equilibration occurs by intra-or transmembrane electron/proton transfer channels driven by free energy gradients.Application of a "half-reaction" strategy in artificial photosynthesis poses similar challenges. In both water oxidation and CO 2 reduction, mechanisms involving one-electron reactions are energetically untenable. They result in • OH on oxidation or CO 2•− o...

Efficient electrochemical water oxidation in neutral and near-neutral systems with a nanoscale silver-oxide catalyst

“…[15,19] Therefore, there is a need to develop low-cost heterogeneous electrocatalysts which remain stable and effective for long-term catalytic operation in metal-ions free neutral or near-neutral aqueous systems. Scheme 1.…”

“…[15,18] This approach demonstrates an attractive scheme for direct solar and chemical energy conversion into renewable fuels and clean energy supplies for power generation or automobile application and avoids the problem related to fossils based energy carriers. [19] In order to establish an electrochemical water splitting system where WOC remains stable in metal free neutral or near-neutral phosphate and borate buffers, or in a CO 2 enriched environment, a water oxidation electrocatalyst is required to operate under pH neutral condition with sustained catalytic activity and high efficiency for oxygen evolution. [15,19] Recently, cobalt and nickel based electrocatalytic materials have been developed in situ in neutral or near-neutral carbonate, phosphate and borate buffers, however these electrocatalytic systems are not very stable in metal free phosphate and borate electrolytes, thus limiting their application for long-term catalytic operations for H 2 generation.…”

A selective and efficient electrocatalyst for carbon dioxide reduction

“…Ideally, one would like to convert CO 2 produced in power plants, refineries and petrochemical plants to fuels or other chemicals through renewable energy utilization [4][5][6] . This desired solution imposes major technological challenges because CO 2 is a fully oxidized and thermodynamically stable molecule 7,8 .…”

Polymer-supported CuPd nanoalloy as a synergistic catalyst for electrocatalytic reduction of carbon dioxide to methane

“…Electrochemical and photoelectrochemical CO 2 reduction to energy-dense hydrocarbon fuels could play a major role and become part of an integrated energy storage strategy, in combination with solar-or wind-generated electricity, as a way to store energy in the chemical bonds of carbon-based fuels (4)(5)(6)(7)(8)(9)(10)(11)(12). Metal-based catalysts for CO 2 reduction have been extensively studied over the last three decades.…”