Exploring efficient and earth-abundant electrocatalysts is of great importance for electrocatalytic and photoelectrochemical hydrogen production. This study demonstrates a novel ternary electrocatalyst of porous cobalt phosphoselenide nanosheets prepared by a combined hydrogenation and phosphation strategy. Benefiting from the enhanced electric conductivity and large surface area, the ternary nanosheets supported on electrochemically exfoliated graphene electrodes exhibit excellent catalytic activity and durability toward hydrogen evolution in alkali, achieving current densities of 10 and 20 mA cm at overpotentials of 150 and 180 mV, respectively, outperforming those reported for transition metal dichalcogenides and first-row transition metal pyrites catalysts. Theoretical calculations reveal that the synergistic effects of Se vacancies and subsequent P displacements of Se atoms around the vacancies in the resulting cobalt phosphoselenide favorably change the electronic structure of cobalt selenide, assuring a rapid charge transfer and optimal energy barrier of hydrogen desorption, and thus promoting the proton kinetics. The overall-water-splitting with 10 mA cm at a low voltage of 1.64 V is achieved using the ternary electrode as both the anode and cathode, and the performance surpasses that of the Ir/C-Pt/C couple for sufficiently high overpotentials. Moreover, the integration of ternary nanosheets with macroporous silicon enables highly efficient solar-driven photoelectrochemical hydrogen production.

Developing highly active electrocatalysts for photoelectrochemical water splitting is critical to bring solar/electrical-to-hydrogen energy conversion processes into reality. Herein, we report a three-dimensional (3D) hybrid electrocatalyst that is constructed through in situ anchoring of CoS nanosheets onto the surface of NiSe nanosheets vertically aligned on an electrochemically exfoliated graphene foil. Benefiting from the synergistic effects between NiSe and CoS, the highly conductive graphene support, and large surface area, the novel 3D hybrid electrode delivers superior electrocatalytic activity toward water reduction in alkaline media, featuring overpotentials of -0.17 and -0.23 V to achieve current densities of 20 and 50 mA cm, respectively, demonstrating an electrocatalytic performance on the top of the NiSe- and CoS-based electrocatalysts as reported in literature. Experimental investigations and theoretical calculations confirm that the remarkable activity of the obtained material results from the unique 3D hierarchical architecture and interface reconstruction between NiSe and CoS through Ni-S bonding, which leads to charge redistribution and thus lowers the energy barrier of hydrogen desorption in the water splitting process. Further integration of the 3D hybrid electrode with a macroporous silicon photocathode enables highly active and sustainable sunlight-driven water splitting in both basic media and real river water. The overall water splitting with 10 mA cm at a low voltage of 1.62 V is achieved using our hybrid as both anode and cathode catalysts, which surpasses that of the Ir/C-Pt/C couple (1.60 V) for sufficiently high overpotentials.

Lithium-sulfur (Li-S) battery is widely recognized as the most promising battery technology for future electric vehicles (EV). To understand the environmental sustainability performance of Li-S battery on future EVs, here a novel life cycle assessment (LCA) model is developed for comprehensive environmental impact assessment of a Li-S battery pack using a graphene sulfur composite cathode and a lithium metal anode protected by a lithium-ion conductive layer, for actual EV applications. The Li-S battery pack is configured with a 61.3 kWh capacity to power a mid-size EV for 320km range. The life cycle inventory model is developed with a hybrid approach, based on our lab-scale synthesis of the graphene sulfur composite, our lab fabrication of Li-S battery cell, and our industrial partner's battery production processes. The impacts of the Li-S battery are assessed using the ReCiPe method and benchmarked with those of a conventional Nickle-Cobalt-Manganese (NCM)-Graphite battery pack under the same driving distance per charge. The environmental impact assessment results illustrate that Li-S battery is more environmentally friendly than conventional NCM-Graphite © 2017. This manuscript version is made available under the Elsevier user license http://www.elsevier.com/open-access/userlicense/1.0/ 2 battery, with 9%~90% lower impact. Finally, the improvement pathways for the Li-S battery to meet the USABC (U.S. Advanced Battery Consortium) targets are presented with the corresponding environmental impact changes. Keyword: Lithium sulfur battery, graphene wrapped sulfur, lithium metal anode, life cycle assessment, environmental impact 1.

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A novel 3D Co-N |P-complex-doped carbon grown on flexible exfoliated graphene foil is designed and constructed for both electrochemical and photoelectrochemical water splitting. The coordination of Co-N active centers hybridized with that of neighboring P atoms enhances the electron transfer and optimizes the charge distribution of the carbon surface, which synergistically promotes reaction kinetics by providing more exposed active sites.

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