The longstanding reliance on fossil fuels as the principal energy source for society has boosted the atmospheric CO₂ concentration to a level that is unprecedented in modern geological history. Since the use of carbon-containing fuels is entrenched in society, controlling the atmospheric CO₂ concentration may ultimately require recycling CO₂ into liquid fuels and commodity chemicals using renewable energy inputs. Arguably the greatest challenge for this vision is to develop efficient CO₂ reduction catalysts. This talk will describe our development of “oxide-derived” metal nanoparticles as electroreduction catalysts. Oxide-derived metal nanoparticles are prepared by electrochemically reducing metal oxide precursors. This procedure results in highly strained metal nanocrystals, as determined by grazing incidence synchrotron x-ray diffraction. I will describe examples of these catalysts that electrochemically reduce CO₂ to CO with exceptional energetic efficiency as well as a catalyst that selectively reduces CO to two-carbon oxygenates. The catalysts operate in water at ambient temperature and pressure and are remarkably robust. The reduction mechanisms will be discussed based on electrokinetic measurements. Metal oxide reduction represents a “top-down” approach to metal nanoparticle synthesis that can result in unique surface structures for catalysis.

The wide-scale implementation of solar and other renewable sources of electricity requires improved means for energy storage. An intriguing strategy in this regard is the reduction of CO₂ to CO, which generates an energy rich commodity chemical that can be coupled to liquid fuel production using Fischer-Tropsch methods. To this end, we have developed an inexpensive Bismuth Carbon Monoxide Evolving Catalyst (Bi-CMEC) that can be formed upon cathodic polarization of an inexpensive carbon or metallic electrode in acidic solutions containing Bi³⁺ ions. This catalyst can be used in conjunction with ionic liquids and other weak organic acids to effect the electrocatalytic conversion of CO₂ to CO with appreciable current density at low overpotential. The systems to be described are selective for production of CO, operating with very high Faradaic efficiency for conversion of CO₂ to this valuable product. As such the ability of this electrocatalyst system to drive production of CO from carbon dioxide is on par with that which has historically only been observed using expensive silver and gold cathodes.

Sustainable energy generation by means of, either photovoltaic conversion, concentrated solar power or wind, will certainly form a significant part of the energy mix in 2025. The intermittency as well as the temporal variation and the regional spread of this energy source, however, requires a means to store and transport energy on a large scale. In this presentation the means of storage will be addressed of sustainable energy transformed into fuels and the prominent role plasma science and technology can play in this great challenge.

The storage of sustainable energy in these so called solar fuels, e.g. hydrocarbons and alcohols, by means of artificial photosynthesis from the feedstock CO₂ and H₂O, will enable a CO₂ neutral power generation infrastructure, which is close to the present infrastructure based on fossil fuels. The challenge will be to achieve power efficient dissociation of CO₂ or H₂O or both, after which traditional chemical conversion (Fisher-Tropsch, Sabatier, etc.) towards fuels can take place.

Most of the research efforts are directed at the splitting of water in hydrogen and oxygen. However, no efficient catalytic or traditional chemical alternative is yet available. A promising route is the dissociation or activation of CO₂ by means of plasma, possible combined with catalysis. Taking advantage of non-equilibrium plasma conditions to reach optimal energy efficiency the FOM institute DIFFER has started its solar fuels program at the beginning of 2012 focusing on CO₂ plasma dissociation into CO and O₂. The plasma is generated in a low loss microwave cavity with microwave powers up to 10 kW using a supersonic expansion to quench the plasma and prevent vibrational-translational relaxation losses. New ideas on the design of the facility and results on power efficient conversion (more then 50%) of large CO₂ flows (up to 75 standard liter per minute with 11% conversion) as determined from calibrated mass spectrometry measurements at low gas temperatures will be presented.