• Energy Research

Hydrogen production increases with increasing Sr content, but at a kinetic penalty; intermediate Sr levels are advantageous for solar thermochemical fuel production.

Supplemental Information can be found online at https://doi.org/10.1016/j.matt. 2020.11.016. [EN] Variable valence oxides of the perovskite crystal structure haveemerged as promising candidates for solar hydrogen productionvia two-step thermochemical cycling. Here, we report the excep-tional efficacy of the perovskite CaTi0.5Mn0.5O3–d(CTM55) for thisprocess. The combination of intermediate enthalpy, rangingbetween 200 and 280 kJ (mol-O) 1, and large entropy, ranging between 120 and 180 J (mol-O) 1K 1, of CTM55 create favorableconditions for water splitting. The oxidation state changes are domi-nated by Mn, with Ti stabilizing the cubic phase and increasing itsreduction enthalpy. A hydrogen yield of 10.0G0.2 mL g 1isachieved in a cycle between 1,350 C (reduction) and 1,150 C(watersplitting) and a total cycle time of 1.5 h, exceeding all previous fuelproduction reports. The gas evolution rate suggests rapid materialkinetics, and, at 1,150 C and higher, a process primarily limited bythe magnitude of the thermodynamic driving force. This research is funded by the U.S. Department of Energy, through the office of Energy Efficiency and Renewable Energy (EERE) contract DE-EE0008089. The supportfrom the European Union’s Horizon 2020 Research And Innovation Programme un-der the Marie Sklodowska-Curie grant agreement no. 746167 is also acknowledged.This work made use of the Jerome B. Cohen X-Ray Diffraction Facility and the Pulsed Laser Deposition Shared Facility at the Materials Research Center at Northwestern University supported by the National Science Foundation MRSEC program (DMR-1720139) and the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF ECCS-1542205). This work additionally made use of the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located at Sector 5 of the Advanced Photon Source (APS) supported by Northwestern University, The Dow Chemical Company, and DuPont de Nemours, Inc. The APS is a U.S. Department of Energy(DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357. The authors acknowledge Dr. Timothy Davenport and Dr. Stephen Wilke for help in thermo-chemical hydrogen production measurements, and graduate student Louis Wangfor assistance with Rietveld refinements and for consultation on thermogravimetric measurements. Peer reviewed

Abstract Recently, CaMnO3 has been proposed as a promising candidate for high temperature thermochemical heat storage. The material reversibly releases oxygen in response to changes in oxygen partial pressure (pO2) in the temperature range (800-1000°C) suitable for Concentrated Solar Power (CSP) plants. However, it undergoes decomposition at pO2

AbstractThe unique properties of solid acid electrolytes, in particular CsH2PO4, are in many ways ideal for fuel cell operation. However, the technology is constrained by high cathode overpotentials. Here a simplified cathode geometry is employed to obtain the fundamental electrochemical parameters (exchange current density and charge transfer coefficient) describing the oxygen reduction reaction (ORR) at the CsH2PO4‐Pt‐gas interface. The parameters are incorporated into a 1D model of the voltage–current characteristics of realistic SAFC cathodes, which reproduced the measured polarization behavior of such cathodes without recourse to fitting adjustable parameters. Following this validation, the model is utilized to evaluate the impact of changes to cathode properties, microstructure, and operating conditions. Of these, the charge transfer coefficient, measured to have a value of ≈0.6 for ORR on Pt in the SAFC cathode environment, is found to have the greatest impact on power output. Nevertheless, even without material modifications, a combination of microstructural and operational modifications are identified with projected performance metrics meeting Department of Energy targets (0.8 V at 300 mA cm−2, and peak power density of 1 W cm−2), albeit at high Pt loadings. However, the analysis indicates that truly meaningful advances will likely necessitate the discovery of alternative ORR catalysts.

High energy efficiency and energy density, together with rapid refuelling capability, render fuel cells highly attractive for portable power generation. Accordingly, polymer-electrolyte direct-methanol fuel cells are of increasing interest as possible alternatives to Li ion batteries. However, such fuel cells face several design challenges and cannot operate with hydrocarbon fuels of higher energy density. Solid-oxide fuel cells (SOFCs) enable direct use of higher hydrocarbons, but have not been seriously considered for portable applications because of thermal management difficulties at small scales, slow start-up and poor thermal cyclability. Here we demonstrate a thermally self-sustaining micro-SOFC stack with high power output and rapid start-up by using single chamber operation on propane fuel. The catalytic oxidation reactions supply sufficient thermal energy to maintain the fuel cells at 500-600 degrees C. A power output of approximately 350 mW (at 1.0 V) was obtained from a device with a total cathode area of only 1.42 cm2.

Combination of nanostructured ceria and nanoscale metal particles leads to unprecedented activity for hydrogen and methane electro-oxidation along with excellent morphological stability.

Doped CeO_2 with a low specific surface area is thermochemically cycled between MO_2 and MO_(2-δ) using H_2O and CO_2 as oxidants. The system rapidly and selectively produces syngas in the absence of a metal catalyst, and CH_4 in the presence of Ni. The Ni catalyst, which permits intermediate C to form on its surface, is proposed to shift the product from syngas to CH_4.