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Several nickel cobalt sulfide (Ni-Co-S) counter electrodes (CEs) are prepared, and the Ni-Co-S nanoparticles are in-situ grown on SnO 2 : F (FTO) transparent conductive glasses via a facile solvothermal process, in which thiourea is used as the sulfurizing reagent. The X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometer are employed to measure the microstructure and composition of the Ni-Co-S CEs. When a proper amount of thiourea is adopted, fine crystalline NiCo 2 S 4 CE is obtained. When the amount of thiourea is small or large, (Ni,Co) 4 S 3 or (Ni,Co) 3 S 4 CE is acquired, respectively. Cyclic voltammetry, electrochemical impedance spectroscopy, Tafel polarization and open-circuit voltage decay (OCVD) measurements all demonstrate that the electrocatalytic activities and electrical conductivities of these Ni-Co-S CEs all approach or exceed those of Pt-pyrolysis CE. Their superior electrochemical performances are further confirmed by fabricating DSSCs with the Ni-Co-S CEs, they display similar or better photo-electric conversion efficiencies to/than the Pt-pyrolysis counterpart. [ABSTRACT FROM AUTHOR]

Herein, we report a one-step hydrothermal procedure to prepare ZnS-CoS microcomposite which was employed as counter electrode (CE) for dye-sensitized solar cells (DSSCs). The microcomposite exhibits a morphology with ZnS microspheres decorated with CoS nanoparticles, and the decoration effect on electrocatalytic activity of prinstine ZnS toward I − /I 3 − redox couple was investigated with cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and Tafel polarization measurements. Experimental results show that ZnS-CoS microcomposite exhibits remarkably enhanced electrocatalytic activity compared with that of pristine ZnS in catalyzing the reduction of I 3 − , and the electrocatalytic activity enhancement closely depends on Co/Zn molar ratio. As a result, the optimized DSSC using ZnS-CoS with a Co/Zn molar ratio of 3: 7 as CE exhibits a highest power conversion efficiency of 6.11%, in comparison with the reference device using Pt CE which shows an efficiency of 7.27%. The enhanced performance compared with DSSC using pristine ZnS CE which has an efficiency of 0.59% can be attributed to the introduction of more electrocatalytic active sites in ZnS-CoS microcomposite. Our study thus provides an effective approach to improve electrocatalytic activity of ZnS and proves its potential suitability as CE for the fabrication of DSSCs. [ABSTRACT FROM AUTHOR]

Herein, we report a bilayer TiO 2 photoanode composed of nanocrystalline TiO 2 (NCT) bottom layer and mixed P25 nanoparticles and large rutile particles (PR) top scattering layer. The present structure performs well in solar light harvesting which is mainly attributed to the fact that the top scattering layer exhibits superior light scattering effect and meanwhile the NCT bottom layer with large dye-loading capacity can make better use of the back-scattered light. Moreover, electrochemical impedance spectroscopy and open circuit voltage decay measurements demonstrate that DSSC based on bilayer photoanode shows faster interfacial electron transfer and slower charge recombination process than that based on NCT monolayer photoanode. These advantages render the DSSCs based on NCT-PR bilayer photoanode exhibiting superior performance under AM1.5G simulated solar irradiation. As an example, by tuning mass ratio between P25 nanoparticles and large rutile particles in the top scattering layer, the DSSC based on NCT-PR bilayer photoanode exhibits an optimum solar energy conversion efficiency of 9.0%, which is about 1.25 times higher than that of monolayer NCT device (7.2%) with the same film thickness. [ABSTRACT FROM AUTHOR]

[Display omitted] • Novel CoSb/NC catalysts are prepared via a novel Sb-modulated strategy. • The feeding amount of Sb salt is tuned to modulate the particle size and pore structure of CoSb/NC catalysts. • CoSb/NC catalysts exhibit enhanced ORR activity and kinetics outperforming the state-of-the-art Pt/C. • CoSb/NC catalysts are electrocatalytically active toward OER. • CoSb/NC catalysts can drive rechargeable Zn-air battery with a high peak power density of 180 mW cm−2. Rational modulation and optimization of structural properties plays a significant role in advancing the electrocatalytic performance of electrocatalysts. In this study, we report a novel Sb-modulated strategy to synthesize novel CoSb/NC catalysts comprised of CoSb alloy supported on nitrogen-doped carbon (denoted as CoSb/NC). Apart from alloying with Co to generate CoSb alloys, we demonstrated that the evaporation of Sb could modulate the particle size and pore structure of CoSb/NC. Such modulation has facilitated the formation of micro/meso-porous structure to accelerate the mass/charge transport and increase the accessibility of active sites, resulting in a highest kinetic current density of 22.6 mA cm−2 at 0.85 V vs. RHE as well as a low Tafel slope of 38 mV dec−1, which even outperforms the state-of-the-art Pt/C. Additionally, CoSb/NC is demonstrated to be electrocatalytic active toward OER with the overpotential to be 430 mV at 10 mA cm−2. Rechargeable Zn-air battery tests reveal that CoSb/NC possesses competitive performance in terms of charge-discharge ability and stability, suggesting its potential application in renewable energy conversion devices. This work provides a novel approach to modulate the structure of nitrogen-doped carbon based materials as efficient oxygen electrocatalysts. [ABSTRACT FROM AUTHOR]

• Co/N-C Zn is prepared via high-temperature gas-transport approach. • The intrinsic structure of Co/ N-C Zn has been greatly modulated by ZnCl 2 treatment. • Co/N-C Zn exhibits enhanced ORR and OER performance. • ORR and OER active sites are determined by control experiments. • Co/N-C Zn can drive liquid and solid-state rechargeable Zn-air battery efficiently. In this study, a facile surface treatment on polypyrrole (PPy) nanofiber with ZnCl 2 solution is employed to fabricate N-doped carbon anchored with metallic Co (denoted as Co/N-C Zn) via gas-transport approach. Structural characterizations reveal that the intrinsic structure of Co/N-C Zn in terms of its morphology, pore structure and defects have been greatly modulated by such a surface treatment, resulting in a higher loading amount of metallic Co, larger surface area and increased pyridinic N and Co-N species as efficient active sites. Benefiting from the structural modulation, Co/N-C Zn exhibits outstanding ORR activity and kinetics with a positive half-wave potential of 0.88 V vs. RHE, a high kinetic current density (J k) value of 36.6 mA cm−2 at 0.85 V vs. RHE, and a small Tafel slope of 55.9 mV dec−1, which even outperforms commercial Pt/C. Moreover, enhanced OER performance is also achieved in Co/N-C Zn , with an overpotential of 280 mV at 10 mA cm−2, surpasses that of commercial RuO 2 (295 mV). Finally, Co/N-C Zn shows promise for substitution of commercial Pt/C and RuO 2 to drive both liquid and solid-state rechargeable Zn-air batteries with high peak power densities of 196 mW cm−2 and 130 mW cm−2. [ABSTRACT FROM AUTHOR]