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The metal free photocatalysts have more environmentally friendly and low-cost advantages but are challenging to find suitable ones. Using the electronic properties of the edge-passivated graphene nanoribbons (EPGNRs) by manipulating the widths and edges, we demonstrate that 5 EPGNRs consisting of metal free elements, which are screened from 10 graphene nanoribbons passivated by H/N/O/F atoms, can achieve high solar-to-hydrogen efficiency in overall water splitting for hydrogen production. After ensuring the energy and thermodynamic stabilities, we construct 16 possible photocatalytic schemes for each EPGNR. At the same time, the feasible ones are selected by calculating charge density distributions, vacuum levels, and the potential energy of the band edges. 9 eligible schemes for overall water splitting are determined and the solar-to-hydrogen efficiencies are calculated according to the overpotentials and band gaps. The highest value of 34.19% is attributed to the H-GNR-O nanoribbon and a larger 38.71% can be boosted by stain engineering, which reveals that the passivated atoms can substantially manipulate the electronic properties and photocatalytic performance of graphene nanoribbons. The calculated Gibbs free energies confirm that the photocatalytic hydrogen and oxygen generations can be driven by the present EPGNRs. Therefore, the newfound metal free EPGNRs are promising for driving overall water splitting for generating hydrogen in a clean way. [Display omitted] • Photocatalytic water splitting schemes are built for five considered nanoribbons. • The highest solar-to-hydrogen efficiency of these schemes can reach 34.19%. • Anisotropic vacuum levels are responsible for the high solar-to-hydrogen efficiency. • Thermodynamic feasibility of the built schemes is ensured by the Gibbs free energies. [ABSTRACT FROM AUTHOR]

A composite anode composing of in-situ exsolved Fe Ni alloy (FNA) nanoparticles and Ruddlesden-Popper perovskite SrLaFeO 4 (SLF) substrate has been prepared by reducing La 0.5 Sr 0.5 Fe 0.8 Ni 0.20 O 3-δ (LSFN) perovskite precursor in humidified H 2 (3% H 2 O) at 800 °C. Roles of FNA and SLF, respectively, in performance and stability of the anode are systematically studied. The electric conductivity of the reduced LSFN and single cell performance of the composite (SLF-FNA) are examined in comparison with those of the SrLaFeO 4-δ (SLFO 4 ) anode alone. The significantly improved performance of the composite anode cell at lower temperatures (<700 °C) may be predominately ascribed to the enhanced electrochemical activity as well as electric conductivity due to the presence of FNA exsolution. The maximum power densities (P max s) of a single cell with the composite anode achieve 0.74, 0.58, 0.40, and 0.25 W cm −2 at 800, 750, 700 and 650 °C, respectively, which is comparable to the performance of Fe Ni-SDC cermets anode. However, the long time stability of the composite anode is superior to that of the Fe Ni-SDC cermets in various fuels, suggesting that SLF-FNA is sulfur-tolerant and coking-tolerant composite anode material, which possess great potentials for future application. The results can be used as guidance for designing high-performance composite anodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). [ABSTRACT FROM AUTHOR]

Cobalt-free composites Nd 0.5 Sr 0.5 Fe 0.8 Cu 0.2 O 3− δ (NSFCu)– x Sm 0.2 Ce 0.8 O 1.9 (SDC) ( x = 0–60 wt%) are investigated as IT-SOFC cathodes. The characteristic properties of cobalt-free composite cathodes comparing to cobalt-based composites are revealed. The DC conductivity and thermal expansion coefficient of the composite cathodes decrease with the content of SDC x , while the polarization resistance R p shows the least value with addition of 40 wt% of SDC. The power density of the single cell with NSFCu-40% SDC composite cathode improved significantly compared with that of undoped NSFCu cathode, with peak values of 488, 623, 849 and 1052 mW cm −2 at 600, 650, 700, and 750 °C, respectively. Moreover, the performance of the composite cathode is stable within testing period of 370 h at 700 °C, indicating that the NSFCu-40% SDC is an excellent cobalt-free composite cathode applied in IT-SOFC. [ABSTRACT FROM AUTHOR]

A new cobalt-free perovskite oxide Pr0.5Sr0.5Fe0.8Cu0.2O3−δ (PSFC) has been synthesized and evaluated as cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs). The chemical compatibility of PSFC with Sm0.2Ce0.8O1.9 (SDC) electrolyte has be proven by XRD, and its electrical conductivity reaches the maximum value of 264.1 S cm−1 at 475 °C. Symmetrical cells with the configuration of PSFC/SDC/PSFC are used for the impedance study and the polarization resistance (Rp) of PSFC cathode is as low as 0.050 Ω cm2 at 700 °C. Single cells, consisting of Ni–YSZ/YSZ/SDC/PSFC structure, are assembled and tested from 550 °C to 800 °C with wet hydrogen (∼3% H2O) as fuel and static air as oxidant. A maximum power density of 1077 mW cm−2 is obtained at 800 °C. All the results suggest that the cobalt-free perovskite oxide PSFC is a very promising cathode material for application in IT-SOFC. [ABSTRACT FROM AUTHOR]

Abstract: A systematic study and evaluation were performed on the effect of scandium doping at the B site of Pr0.6Sr0.4Co0.2Fe0.8O3−δ (PSCF) on key material properties as cathode for intermediate temperature solid oxide fuel cells (IT-SOFC). The doped products Pr0.6Sr0.4(Co0.2Fe0.8)(1−x)Sc x O3−δ (PSCFS x , x=0.0–0.2) retained perovskite structure confirmed by X-ray diffraction, and their particles were smaller than the non-doped materials as evidenced by TEM. The electrical conductivity (EC) of PSCFS x decreased with increasing Sc3+ content, but EC values were still larger than 100 S cm−1 in temperature range of 300–800 °C as x ≤ 0.1. The thermal expansion coefficients (TEC) of PSCFS x were observed to generally decrease with increasing x especially at lower temperature range of 50–600 °C. In addition, the AC impedance revealed better electrochemical performance of PSCFS x cathode as x ≤ 0.1 than that of the undoped sample PSCF. Therefore, PSCFS x (x ≤ 0.1) shows some potential as cathode electrode for IT-SOFC. The function of Sc3+ dopant was tentatively elucidated and discussed. [Copyright &y& Elsevier]

A hetero-structured composite porous cathode has been prepared by mixing 90 wt% single-phase perovskite (SP 1 1 SP: Single-phase perovskite.) La 0·6 Sr 0·4 Co 0·2 Fe 0·8 O 3-δ (LSCF113 2 2 LSCF113: La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3-δ.) and 10 wt% Ruddlesden-Popper layered perovskite (RP 3 3 RP: Ruddlesden-Popper layered perovskite.) LaSrCo 0 · 2 Fe 0·8 O 4-δ (LSCF214 4 4 LSCF214: LaSrCo 0.2 Fe 0.8 O 4-δ.) nano-powders. The powders were separately synthesized by wet chemical coprecipitation (CP 5 5 CP: Wet chemical coprecipitation.) method, and subsequently mixed by ball-milling to obtain the composite CP-LSCF214-113 cathode with RP/SP hetero-interface. The hetero-interface has been confirmed by XRD and TEM. The polarization impedance (R p) of symmetrical cell with the composite cathode achieved 0.024 and 0.147 Ω cm2 at 800 and 700 °C, decreasing 65% and 72% of the cathode impedance of CP-LSCF113, respectively. An anode supported SOFC with the CP-LSCF214-113 composite cathode achieved maximum power density of 1.02 W cm−2 at 800 °C. The CP-LSCF214-113 based single cell also showed acceptable stability similar to CP-LSCF113 based cell over 100 h at 700 °C. Moreover, the CP-LSCF214-113 effectively inhibits the coarsening of grains and the growth of RP phase. The solid state reaction (SSR 6 6 SSR: Solid state reaction.) method was used for comparison. Our results revealed that the CP method combined with ball-milling and subsequent calcining is an effective way to construct RP/SP hetero-interface in porous cathodes for intermediate temperature solid oxide fuel cells (IT-SOFCs). [Display omitted] • LSCF214-113 hetero-structures were constructed by a facial wet chemical route. • The decrease of LSCF214-113 particle size increased TPB for ORR reaction. • LSCF214-113 cathode show excellent low polarization resistance of 0.024 Ω cm2. • Composite cathode achieved power density as high as 1.02 W cm−2 at 800 °C. [ABSTRACT FROM AUTHOR]