Strongly coupling of amorphous/crystalline reduced FeOOH/α-Ni(OH)2 heterostructure for extremely efficient water oxidation at ultra-high current density.

Development of Fe-Ni-based electrocatalysts with high efficiency and stability remains a foremost challenge in the research for oxygen evolution reaction (OER) under high-current-density. Herein, a fast reduction strategy is developed for synthesis of strongly coupled crystalline α-Ni(OH)2 with amorphous reduced FeOOH (r-FeOOH) heterostructure grown on Ni foam (r-FeOOH/α-Ni(OH)2/NF). The obtained r-FeOOH/α-Ni(OH)2 with particle sizes around ~ 10 nm is coated orderly on the 3D NF surface in this hybrid. Benefitting from the strong coupling effects between r-FeOOH and α-Ni(OH)2, low potentials of 1.62 and 1.66 V at ultra-high current densities of 1,000 and 1,500 mA cm-2, as well as a robust stability over 10 h at 1,500 mA cm-2 in alkaline electrolyte are achieved in 3D r-FeOOH/α-Ni(OH)2/NF. Such a high OER performance is almost the best among all previously reported Fe-Ni-based OER electrocatalysts. Experimental results revealed that the NiOOH species is the real OER active phase in the 3D r-FeOOH/α-Ni(OH)2/NF. Further, bifunctional 3D r-FeOOH/α-Ni(OH)2 in alkaline electrolyzer delivers low cell voltages of 2.32 and 2.78 V to attain 500 and 1,000 mA cm-2 toward the overall-water-splitting, surpassing the benchmark Pt/C-Ir/C/NF system.

Highly Effective Electrochemical Exfoliation of Ultrathin Tantalum Disulfide Nanosheets for Energy-Efficient Hydrogen Evolution Electrocatalysis.

Developing highly efficient transition metal dichalcogenide electrocatalysts would be significantly beneficial for the electrocatalytic hydrogen evolution reaction (HER) from water splitting. Herein, we reported novel ultrathin tantalum disulfide nanosheets (TaS2 NSs) prepared by electrochemically exfoliating bulk TaS2 with an alternating voltage in an acidic electrolyte. The obtained TaS2 NS electrocatalyst possessed an ultrathin structure with a lateral size of 2 µm and a thickness of ∼3 nm. Owing to the unique 2D structure, the achieved TaS2 NSs displayed remarkable electrocatalytic activity toward the HER by a small overpotential of 197 mV at 10 mA cm-2 and a small Tafel slope of 100 mV dec-1 in acidic solution, much lower than those of TaS2 (>547 mV and 216 mV dec-1, respectively) and other reported TaS2-based HER electrocatalysts. Furthermore, highly efficient full water splitting could be realized with two electrodes in which TaS2 NSs acted as the cathode while Ir/C served as the anode, with help of two AA size batteries or solar cells. By replacing the oxygen evolution reaction with the urea oxidation reaction (UOR), bifunctional TaS2 NSs enabled an energy-effective HER process in the cathode and UOR process in the anode with decreased applied potential.

Nanoconfined Tin Oxide within N-Doped Nanocarbon Supported on Electrochemically Exfoliated Graphene for Efficient Electroreduction of CO2 to Formate and C1 Products.

Developing low-cost and effective electrocatalysts for electrochemical reduction of CO2 (CO2ER) is critical to CO2 conversion and utilization. Herein, we report a novel two-dimensional (2D) confined electrocatalyst composed of core-shell structured tin oxide nanoparticles (NPs) encapsulated into N-doped carbon (NC) supported on electrochemically exfoliated graphene (SnO2⊃NC@EEG) prepared by in situ carbonization of a 2-methylimidazole/SnO2 complex@poly(vinyl pyrrolidone) (PVP)-modified EEG precursor. The SnO2 NPs with an average size of ∼10 nm are confined in the NC shells with a thickness of 0.7 nm derived from 2-methylimidazole. The resulting 2D confined electrocatalyst significantly enhances the CO2ER performance with a small onset potential of -0.45 V, and high Faradic efficiencies of 81.2 and 93.2% for HCOO- and C1 products at -1.2 V, respectively, which is far superior to other reported SnO2/carbon-based CO2ER hybrids. The superb CO2ER catalytic activity of the SnO2⊃NC@EEG has resulted from the positive effect of N dopants and a strong confinement effect, which significantly expedites the CO2 adsorption associated with charge transfer from the NC to SnO2 NPs during CO2ER electrocatalysis.

Confined carburization-engineered synthesis of ultrathin nickel oxide/nickel heterostructured nanosheets for enhanced oxygen evolution reaction.

Low-cost and highly effective transition metal oxides are being widely researched as one of the most promising electrocatalysts for the oxygen evolution reaction (OER). However, traditional transition metal oxides suffer from sluggish reaction kinetics due to their intrinsically poor electronic conductivity. Herein, we demonstrate a facile polydopamine-assisted carburization strategy for the confined synthesis of novel NiOx/Ni ultrathin heterostructured nanosheets. Benefiting from the large exposed surface area and fast charge transfer, the obtained ultrathin NiOx/Ni heterostructured nanosheets exhibit an overpotential of 358 mV at a current density of 10 mA cm-2 and a small Tafel slope of 51 mV dec-1, outperforming other reported representative nickel oxide based materials and commercial Ir/C catalysts. In addition, a sustainable and efficient overall water-splitting electrolyzer integrated ultrathin NiOx/Ni nanosheets with commercial Pt/C can be effectively and stably driven by solar cells.

High-index faceted binary-metal selenide nanosheet arrays as efficient 3D electrodes for alkaline hydrogen evolution.

Exploring highly active and durable Earth-abundant electrocatalysts to replace the precious noble metals holds great promise for the hydrogen evolution reaction (HER) from water splitting. Herein, a novel (110) high-index faceted binary-metal selenide (FeNiSe) nanosheet array grown on electrochemically exfoliated graphene foil (FeNiSe-NS/EG) is developed from its vertically-oriented NiFe-LDH nanosheet/EG precursor through a low-temperature selenization reaction. Benefiting from its unique 3D configuration and enhanced electrical conductivity, the obtained FeNiSe-NS/EG electrode exhibits excellent electrocatalytic activity toward the HER with small overpotentials of -187 and -222 mV at current densities of 10 and 20 mA cm-2, a low Tafel slope of 65 mV dec-1, and remarkable long term stability in alkaline media, outperforming the recently reported NiFe-based non-precious metal HER catalysts. Theoretical calculations and experimental results reveal that the synergistic effects of the exposed (110) high-index facets and Fe dopants give rise to a greatly enhanced HER performance.

Strongly Coupled 3D N-Doped MoO2/Ni3S2 Hybrid for High Current Density Hydrogen Evolution Electrocatalysis and Biomass Upgrading.

Developing noble metal-free electrocatalysts toward hydrogen evolution reaction (HER) that can work well at ultrahigh current density are crucial components in renewable energy technologies. Herein, we have reported a strongly coupled 3D hybrid electrocatalyst, which consists of N-doped MoO2 with Ni3S2 grown on Ni foam (N-MoO2/Ni3S2 NF) through an annealing treatment, followed by a thermal ammonia reaction. This N-MoO2/Ni3S2 with a particle size of ∼50 nm was evenly grown on the Ni substrate in this 3D hybrid system. Benefiting from the strong coupling effect, the N-MoO2/Ni3S2 NF exhibited a high HER performance in basic media, with a small value of the Tafel slope (76 mV dec-1) and a low potential of 517 mV at 1000 mA cm-2, which was superior to that of Pt/C (631 mV at 1000 mA cm-2). Experimental results revealed that constructing a coupling interface between N-MoO2 and Ni3S2 facilitated the absorption and dissociation of water molecules, consequently boosting the HER activity. Additionally, the 3D N-MoO2/Ni3S2 NF hybrid could act as a bifunctional electrode for both anode (biomass upgrading) and cathode (HER), which only required a lower potential of 2.08 V at 100 mA cm-2 as compared to the overall water splitting (2.25 V) and achieved a high biomass conversion ratio of over 90%. Moreover, substituting oxygen evolution reaction by urea oxidation reaction also can assist energy-saving hydrogen evolution for 3D N-MoO2/Ni3S2 NF.

Atomically dispersed nickel-nitrogen-sulfur species anchored on porous carbon nanosheets for efficient water oxidation.

Developing low-cost electrocatalysts to replace precious Ir-based materials is key for oxygen evolution reaction (OER). Here, we report atomically dispersed nickel coordinated with nitrogen and sulfur species in porous carbon nanosheets as an electrocatalyst exhibiting excellent activity and durability for OER with a low overpotential of 1.51 V at 10 mA cm-2 and a small Tafel slope of 45 mV dec-1 in alkaline media. Such electrocatalyst represents the best among all reported transition metal- and/or heteroatom-doped carbon electrocatalysts and is even superior to benchmark Ir/C. Theoretical and experimental results demonstrate that the well-dispersed molecular S|NiNx species act as active sites for catalyzing OER. The atomic structure of S|NiNx centers in the carbon matrix is clearly disclosed by aberration-corrected scanning transmission electron microscopy and synchrotron radiation X-ray absorption spectroscopy together with computational simulations. An integrated photoanode of nanocarbon on a Fe2O3 nanosheet array enables highly active solar-driven oxygen production.

3D Edge-Enriched Fe3 C@C Nanocrystals with a Core-Shell Structure Grown on Reduced Graphene Oxide Networks for Efficient Oxygen Reduction Reaction.

The design of highly active, stable, and low-cost oxygen reduction reaction (ORR) electrocatalysts to replace platinum-based materials is crucial to the development of renewable energy technologies. Herein, novel 3D edge-enriched Fe3 C@C nanocrystals with a core-shell structure grown on reduced graphene oxide (rGO) networks (Fe3 C@C/rGO) are reported as highly efficient and stable electrocatalysts for the ORR. The rGO nanosheets act as a host and provide vital support for local growth of edge-enriched Fe3 C@C nanocrystals, leading to a large surface area of 263 m2 g-1 and superstable hybrid structure. The unique structural design of the Fe3 C@C/rGO hybrid enables fast mass transport and a substantial number of exposed active edge sites for electrocatalytic reaction. The Fe3 C@C/rGO hybrid exhibits excellent ORR catalytic activity, with a high positive onset potential close to 1.0 V, a Tafel slope of 65 mV dec-1 , and excellent durability with only about 8 % current density decay at 0.8 V after 20 000 s continuous operation, which is superior to that of commercial Pt/C catalyst in an alkaline electrolyte.

Predictive modeling of battery degradation and greenhouse gas emissions from U.S. state-level electric vehicle operation.

Electric vehicles (EVs) are widely promoted as clean alternatives to conventional vehicles for reducing greenhouse gas (GHG) emissions from ground transportation. However, the battery undergoes a sophisticated degradation process during EV operations and its effects on EV energy consumption and GHG emissions are unknown. Here we show on a typical 24 kWh lithium-manganese-oxide-graphite battery pack that the degradation of EV battery can be mathematically modeled to predict battery life and to study its effects on energy consumption and GHG emissions from EV operations. We found that under US state-level average driving conditions, the battery life is ranging between 5.2 years in Florida and 13.3 years in Alaska under 30% battery degradation limit. The battery degradation will cause a 11.5-16.2% increase in energy consumption and GHG emissions per km driven at 30% capacity loss. This study provides a robust analytical approach and results for supporting policy making in prioritizing EV deployment in the U.S.

Ternary Porous Cobalt Phosphoselenide Nanosheets: An Efficient Electrocatalyst for Electrocatalytic and Photoelectrochemical Water Splitting.

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-2 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-2 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.

Integrated Hierarchical Cobalt Sulfide/Nickel Selenide Hybrid Nanosheets as an Efficient Three-dimensional Electrode for Electrochemical and Photoelectrochemical Water Splitting.

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 Co9S8 nanosheets onto the surface of Ni3Se2 nanosheets vertically aligned on an electrochemically exfoliated graphene foil. Benefiting from the synergistic effects between Ni3Se2 and Co9S8, 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-2, respectively, demonstrating an electrocatalytic performance on the top of the Ni3Se2- and Co9S8-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 Ni3Se2 and Co9S8 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-2 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.

A TiO2 nanotube network electron transport layer for high efficiency perovskite solar cells.

The electron transport layer (ETL) plays a critical role in high efficiency perovskite solar cells. In this study, an anodic TiO2 nanotube film was transformed into a TiO2 nanotube network film, which maintained its advantage as an efficient ETL for perovskite solar cells. Compared with the mesoporous TiO2 nanoparticle ETL, the TiO2 nanotube network ETL can increase the efficiency of perovskite solar cells by 26.6%, which is attributed to its superior charge collection property and light trapping ability. The results confirm the importance of optimizing the electron collecting layer and suggest another way to design and fabricate novel perovskite solid state solar cells, potentially by using a TiO2 nanotube network film as an alternative high efficiency electrode.

Efficient Electrochemical and Photoelectrochemical Water Splitting by a 3D Nanostructured Carbon Supported on Flexible Exfoliated Graphene Foil.

A novel 3D Co-Nx |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-Nx 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.

3D dual-confined sulfur encapsulated in porous carbon nanosheets and wrapped with graphene aerogels as a cathode for advanced lithium sulfur batteries.

Although lithium-sulfur (Li-S) batteries have attracted much attention due to their high theoretical specific energy and low cost, their practical applications have been severely hindered by poor cycle life, inadequate sulfur utilization, and the insulating nature of sulfur. Here, we report a rationally designed Li-S cathode with a dual-confined configuration formed by confining sulfur in 2D carbon nanosheets with an abundant porous structure followed by 3D graphene aerogel wrapping. The porous carbon nanosheets act as the sulfur host and suppress the diffusion of polysulfide, while the graphene conductive networks anchor the sulfur-adsorbed carbon nanosheets, providing pathways for rapid electron/ion transport and preventing polysulfide dissolution. As a result, the hybrid electrode exhibits superior electrochemical performance, including a large reversible capacity of 1328 mA h g(-1) in the first cycle, excellent cycling stability (maintaining a reversible capacity of 647 mA h g(-1) at 0.2 C after 300 cycles) with nearly 100% Coulombic efficiency, and a high rate capability of 512 mA h g(-1) at 8 C for 30 cycles, which is among the best reported rate capabilities.

Band gap opening and semiconductor-metal phase transition in (n, n) single-walled carbon nanotubes with distinctive boron-nitrogen line defect.

Band gap opening and modulating are critical in dictating the functionalities of single walled carbon nanotubes (SWCNTs) in a broad array of nano-devices. Using first-principles density functional theory calculations, a class of semiconducting armchair SWCNTs with a distinctive BN line defect are studied, showing a super capacity to open the band gap of (4, 4) SWCNT to as large as 0.86 eV, while the opened band gap are found decreasing with the increasing diameters of SWCNTs. The opened band gap of SWCNTs can also be successfully modulated through both mechanical and electrical approaches by applying compressive uniaxial strain and electric field. This study provides novel insights into the large band gap opening and modulating of SWCNTs and could be useful in facilitating future applications of SWCNTs in electronic, optical and thermoelectric devices.

Life Cycle Assessment of Titania Perovskite Solar Cell Technology for Sustainable Design and Manufacturing.

Perovskite solar cells have attracted enormous attention in recent years due to their low cost and superior technical performance. However, the use of toxic metals, such as lead, in the perovskite dye and toxic chemicals in perovskite solar cell manufacturing causes grave concerns for its environmental performance. To understand and facilitate the sustainable development of perovskite solar cell technology from its design to manufacturing, a comprehensive environmental impact assessment has been conducted on titanium dioxide nanotube based perovskite solar cells by using an attributional life cycle assessment approach, from cradle to gate, with manufacturing data from our laboratory-scale experiments and upstream data collected from professional databases and the literature. The results indicate that the perovskite dye is the primary source of environmental impact, associated with 64.77% total embodied energy and 31.38% embodied materials consumption, contributing to more than 50% of the life cycle impact in almost all impact categories, although lead used in the perovskite dye only contributes to about 1.14% of the human toxicity potential. A comparison of perovskite solar cells with commercial silicon and cadmium-tellurium solar cells reveals that perovskite solar cells could be a promising alternative technology for future large-scale industrial applications.

A multilayered silicon-reduced graphene oxide electrode for high performance lithium-ion batteries.

A multilayered structural silicon-reduced graphene oxide electrode with superior electrochemical performance was synthesized from bulk Si particles through inexpensive electroless etching and graphene self-encapsulating approach. The prepared composite electrode presents a stable charge-discharge performance with high rate, showing a reversible capacity of 2787 mAh g(-1) at a charging rate of 100 mA g(-1), and a stable capacity over 1000 mAh g(-1) was retained at 1 A g(-1) after 50 cycles with a high columbic efficiency of 99% during the whole cycling process. This superior performance can be attributed to its novel multilayered structure with porous Si particles encapsulated, which can effectively accommodate the large volume change during the lithiation process and provide increased electrical conductivity. This facile low-cost approach offers a promising route to develop an optimized carbon encapsulated Si electrode for future industrial applications.

Enhanced photovoltaic performance of perovskite CH3NH3PbI3 solar cells with freestanding TiO2 nanotube array films.

Freestanding TiO2 nanotube array films are fabricated and first applied as electrodes in perovskite CH3NH3PbI3 sensitized solar cells. The device demonstrates improved light absorption with more than 90% of light absorbed in the whole visible range and a reduced charge recombination rate, leading to a significant improvement of the photocurrent and efficiency. This study suggests a promising way of improving the conversion efficiency of perovskite solar cells through novel electrodes.

A scalable graphene sulfur composite synthesis for rechargeable lithium batteries with good capacity and excellent columbic efficiency.

Sulfur nanoparticles wrapped with a conductive graphene framework was synthesized with a high sulfur loading through a scalable one-step process. The graphene-coated sulfur nanostructured composite, when used as cathode for lithium sulfur battery, shows a reversible capacity of 808 mAh g(-1) at a rate of 210 mA g(-1) and an average columbic efficiency of ∼98.3% over 100 cycles. It is found that graphene oxide (GO) with a porous structure offers flexible confinement function that helps prevent the loss of active materials, thus extending the cycling life of the electrode. Moreover, reduced graphene oxide provides a conductive network surrounding the sulfur particles, which facilitates both electron transport and ion transportation. This novel one-step, all-solution-based process is scalable and provides a promising approach for potential industrial applications.

Life cycle environmental impact of high-capacity lithium ion battery with silicon nanowires anode for electric vehicles.

Although silicon nanowires (SiNW) have been widely studied as an ideal material for developing high-capacity lithium ion batteries (LIBs) for electric vehicles (EVs), little is known about the environmental impacts of such a new EV battery pack during its whole life cycle. This paper reports a life cycle assessment (LCA) of a high-capacity LIB pack using SiNW prepared via metal-assisted chemical etching as anode material. The LCA study is conducted based on the average U.S. driving and electricity supply conditions. Nanowastes and nanoparticle emissions from the SiNW synthesis are also characterized and reported. The LCA results show that over 50% of most characterized impacts are generated from the battery operations, while the battery anode with SiNW material contributes to around 15% of global warming potential and 10% of human toxicity potential. Overall the life cycle impacts of this new battery pack are moderately higher than those of conventional LIBs but could be actually comparable when considering the uncertainties and scale-up potential of the technology. These results are encouraging because they not only provide a solid base for sustainable development of next generation LIBs but also confirm that appropriate nanomanufacturing technologies could be used in sustainable product development.