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The flame-made nanostructured agglomerates achieved ca. 200% higher syngas production rates and the highest redox capacity so far reported for ceria.

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Efficient storage of solar and wind power is one of the most challenging tasks still limiting the utilization of the prime but intermittent renewable energy sources. The direct storage of concentrated solar power in renewable fuels via thermochemical splitting of water and carbon dioxide on a redox material is a scalable approach with up to 54% solar-to-fuel conversion efficiency. Despite progress, the search for earth-abundant materials that can provide and maintain high H 2 and CO production rates over long period of high-temperature cycles continues. Here, we report a strategy to unlock the use of manganese, the 12th most abundant element in the Earth's crust, for thermochemical synthesis of solar fuels, achieving superior thermochemical stability, oxygen exchange capacity, and up to seven times higher mass-specific H 2 and CO yield than cerium dioxide. We observe that incorporation of a small fraction of cerium ions in the manganese (II,III) oxide crystal lattice drastically increases its oxygen ion mobility, allowing its reduction from oxide to carbide during methane partial oxidation with simultaneous Ce exsolution. High CO 2 and H 2 O splitting rates are achieved by re-oxidation of the carbide to manganese (II) oxide with simultaneous reincorporation of the cerium ions. We demonstrate that the oxide to carbide reaction is highly reversible achieving remarkable CO 2 splitting rates over 100 thermochemical cycles of methane partial oxidation and CO 2 splitting, and preserving the initial oxygen exchange capacity of 0.65 mol O − mol Mn 1 and 89% of the fuel production rates. Due to this extraordinarily high reversible oxygen exchange capacity, the 3% Ce-doped manganese oxide achieves an average mass-specific CO yield for CO 2 splitting of 17.72 mmol CO g −1 , which is significantly higher than that previously achieved in thermochemical redox cycles. More generally, these findings suggest that incorporation of small soluble amounts of cerium in earth-abundant transition metal oxides like manganese oxide is a powerful approach to enable solar thermochemical fuel synthesis.

The reaction pathway of sulfur dioxide electro-oxidation on platinum and gold substrates is investigated here using a combination of static and rotating electrode voltammetric methods. A gold electrocatalyst does not need to be sulfur modified in order to display high activity, meaning the substrate is inherently more active than platinum. Analysis of diffusion behavior and reaction order on these substrates suggests that both kinetic and diffusion limitations control oxidation on each electrode. However, it is proposed that a similar oxidation pathway, involving adsorption and subsequent oxidation of sulfur dioxide on the electrode surface, is followed for an activated electrode. Mass changes were monitored at the electrode surface using an electrochemical quartz crystal microbalance, and both in-and ex-situ observations support this pathway proposal.Sulfur dioxide electrochemistry has been an area of widely varied research interest over the last few decades. The reaction has been of interest most recently due to its poisoning effect on the oxygen reduction reaction in fuel cells. 1 The electrochemical oxidation of sulfur dioxide is also of great relevance to the hybrid sulfur (HyS) cycle, a water splitting cycle for large scale hydrogen production. The greatest advantage the HyS cycle has over conventional electrolysis is the reduction in the required electrical input through the use of sulfur intermediates. Hydrogen and oxygen evolution steps are split into electrical and thermal components, respectively, and both energy inputs can be supplied using solar sources. 2 Hydrogen is evolved as the cathodic reaction of an acid electrolyser, while, sulfur dioxide is oxidized to sulfuric acid in the anodic compartment; i.e.,+ + 2e − → H 2 (g) E o = 0.000 V [1] SO 2 (aq) + 2H 2 O → H 2 SO 4 (aq) + 2H + + 2e − E o = 0.157 V [2] SO 2 (aq) + 2H 2 O → H 2 SO 4 (aq) + H 2 (g) E o = 0.157 V [3]