2017 Vol. 2, No. 2

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Editorial
Green energy for green future
2017, 2(2) doi: 10.1016/j.gee.2017.03.003
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Commentary
Bio-inspired photosystem for green energy
Xuehai Yan
2017, 2(2) doi: 10.1016/j.gee.2016.11.009
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Viewpoint
Amazing long-lived lifetime
Weiwei Zhang, Wei-Hong Zhu
2017, 2(2): 67-69. doi: 10.1016/j.gee.2016.12.001
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Review article
Advanced electron microscopy characterization of nanomaterials for catalysis
Dong Su
2017, 2(2): 70-83. doi: 10.1016/j.gee.2017.02.001
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Transmission electron microscopy (TEM) has become one of the most powerful techniques in the fields of material science, inorganic chemistry and nanotechnology. In terms of resolutions, advanced TEM may reach a high spatial resolution of 0.05 nm, a high energy-resolution of 7 meV. In addition, in situ TEM can help researchers to image the process happened within 1 ms. This paper reviews the recent technical progresses of applying advanced TEM characterization on nanomaterials for catalysis. The text is organized based on the perspective of application: for example, size, composition, phase, strain, and morphology. The electron beam induced effect and in situ TEM are also introduced. I hope this review can help the scientists in related fields to take advantage of advanced TEM to their own researches.
Biomass derived porous nitrogen doped carbon for electrochemical devices
Litao Yan, Jiuling Yu, Jessica Houston, Nancy Flores, Hongmei Luo
2017, 2(2): 84-99. doi: 10.1016/j.gee.2017.03.002
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Biomass derived porous nanostructured nitrogen doped carbon (PNC) has been extensively investigated as the electrode material for electrochemical catalytic reactions and rechargeable batteries. Biomass with and without containing nitrogen could be designed and optimized to prepare PNC via hydrothermal carbonization, pyrolysis, and other methods. The presence of nitrogen in carbon can provide more active sites for ion absorption, improve the electronic conductivity, increase the bonding between carbon and sulfur, and enhance the electrochemical catalytic reaction. The synthetic methods of natural biomass derived PNC, heteroatomic co- or tri-doping into biomass derived carbon and the application of biomass derived PNC in rechargeable Li/Na batteries, high energy density Li–S batteries, supercapacitors, metal-air batteries and electrochemical catalytic reaction (oxygen reduction and evolution reactions, hydrogen evolution reaction) are summarized and discussed in this review. Biomass derived PNCs deliver high performance electrochemical storage properties for rechargeable batteries/supercapacitors and superior electrochemical catalytic performance toward hydrogen evolution, oxygen reduction and evolution, as promising electrodes for electrochemical devices including battery technologies, fuel cell and electrolyzer.
Developing new understanding of photoelectrochemical water splitting via in-situ techniques: A review on recent progress
Jiajie Cen, Qiyuan Wu, Mingzhao Liu, Alexander Orlov
2017, 2(2): 100-111. doi: 10.1016/j.gee.2017.03.001
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Photoelectrochemical (PEC) water splitting is a promising technology for solar hydrogen production to build a sustainable, renewable and clean energy economy. Given the complexity of the PEC water splitting processes, it is important to note that developing in-situ techniques for studying PEC water splitting presents a formidable challenge. This review is aimed at highlighting advantages and disadvantages of each technique, while offering a pathway of potentially combining several techniques to address different aspects of interfacial processes in PEC water splitting. We reviewed recent progress in various techniques and approaches utilized to study PEC water splitting, focusing on spectroscopic and scanning-probe methods.
Research paper
Integrated Ni-P-S nanosheets array as superior electrocatalysts for hydrogen generation
Haoxuan Zhang, Haibo Jiang, Yanjie Hu, Hao Jiang, Chunzhong Li
2017, 2(2): 112-118. doi: 10.1016/j.gee.2016.12.004
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Searching for efficient and robust non-noble electrocatalysts for hydrogen generation is extremely desirable for future green energy systems. Here, we present the synthesis of integrated Ni-P-S nanosheets array including Ni2P and NiS on nickel foam by a simple simultaneous phosphorization and sulfurization strategy. The resultant sample with optimal composition exhibits superior electrocatalytic performance for hydrogen evolution reaction (HER) in a wide pH range. In alkaline media, it can generate current densities of 10, 20 and 100 mA cm−2 at low overpotentials of only −101.9, −142.0 and −207.8 mV with robust durability. It still exhibits high electrocatalytic activities even in acid or neutral media. Such superior electrocatalytic performances can be mainly attributed to the synergistic enhancement of the hybrid Ni-P-S nanosheets array with integration microstructure. The kind of catalyst gives a new insight on achieving efficient and robust hydrogen generation.
NixWO2.72 nanorods as an efficient electrocatalyst for oxygen evolution reaction
Zheng Xi, Adriana Mendoza-Garcia, Huiyuan Zhu, MiaoFang Chi, Dong Su, Daniel P. Erdosy, Junrui Li, Shouheng Sun
2017, 2(2): 119-123. doi: 10.1016/j.gee.2017.01.001
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NixWO2.72 nanorods (NRs) are synthesized by a one-pot reaction of Ni(acac)2 and WCl4. In the rod structure, Ni(II) intercalates in the defective perovskite-type WO2.72 and is stabilized. The NixWO2.72 NRs show the x-dependent electrocatalysis for the oxygen evolution reaction (OER) in 0.1 M KOH with Ni0.78WO2.72 being the most efficient, even outperforming the commercial Ir-catalyst. The synthesis is not limited to NixWO2.72 but can be extended to MxWO2.72 (M = Co, Fe) as well, providing a new class of oxide-based catalysts for efficient OER and other energy conversion reactions.
Facile microwave-assisted ionic liquid synthesis of sphere-like BiOBr hollow and porous nanostructures with enhanced photocatalytic performance
Zhigang Chen, Jie Zeng, Jun Di, Dexiang Zhao, Mengxia Ji, Jiexiang Xia, Huaming Li
2017, 2(2): 124-133. doi: 10.1016/j.gee.2017.01.005
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In this work, two kinds of self-assembled hierarchical BiOBr microcrystals were rapidly synthesized through a simple microwave-assisted route in the presence of reactable ionic liquid 1-hexadecyl-3-methylimidazolium bromide ([C16mim]Br). These porous and hollow BiOBr microspheres were obtained via a facile solvothermal method with or without polyvinyl pyrrolidone (PVP), respectively. During the synthetic process, ionic liquid [C16mim]Br played as solvent, reactant and template at the same time. Moreover, the BiOBr hollow and porous microspheres exhibited outstanding photocatalytic activities for the degradation of rhodamine B (RhB) under visible light irradiation. A possible photocatalytic mechanism was also discussed in detail. It can be assumed that the higher photocatalytic activities of BiOBr porous microspheres materials could be ascribed to the novel structure, larger specific surface area, narrower band gap structure and smaller particle size.
Three-dimensional hierarchical MoS2/CoS2 heterostructure arrays for highly efficient electrocatalytic hydrogen evolution
Canbin Ouyang, Shi Feng, Jia Huo, Shuangyin Wang
2017, 2(2): 134-141. doi: 10.1016/j.gee.2017.01.004
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Developing non-expensive, highly active and highly stable electrocatalysts for hydrogen evolution has aroused extensive attention, owing to the necessity of novel clean and sustainable energy carriers. In this paper, we report a synthesis of free-standing three-dimensional hierarchical MoS2/CoS2 heterostructure arrays through a convenient process. The investigation of electrocatalytic HER performance suggests that the MoS2/CoS2 hybrid catalyst exhibits significant enhancement in HER (onsetpotential and potential at a current density of 100 mA cm−2 are 20 mV and 125 mV, respectively) and superior durability (no shift of current density is observed after a continuous scanning of 3000 times) compared with individual CoS2 and MoS2. The superior HER performance was attributed to the formation of the interface between CoS2 and MoS2 through the electrochemical characterization, Raman, XPS analysis, and the control experiment. The lower onsetpotential, higher current density, excellent durability, and the free-standing structure of the three-dimensional hierarchical MoS2/CoS2 heterostructure array make it a promising cathode catalyst suitable for widespread application.
Highly efficient cobalt-doped carbon nitride polymers for solvent-free selective oxidation of cyclohexane
Yu Fu, Wangcheng Zhan, Yanglong Guo, Yun Guo, Yunsong Wang, Guanzhong Lu
2017, 2(2): 142-150. doi: 10.1016/j.gee.2017.01.006
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Selective oxidation of saturated hydrocarbons with molecular oxygen has been of great interest in catalysis, and the development of highly efficient catalysts for this process is a crucial challenge. A new kind of heterogeneous catalyst, cobalt-doped carbon nitride polymer (g-C3N4), was harnessed for the selective oxidation of cyclohexane. X-ray diffraction, Fourier transform infrared spectra and high resolution transmission electron microscope revealed that Co species were highly dispersed in g-C3N4 matrix and the characteristic structure of polymeric g-C3N4 can be retained after Co-doping, although Co-doping caused the incomplete polymerization to some extent. Ultraviolet–visible, Raman and X-ray photoelectron spectroscopy further proved the successful Co doping in g-C3N4 matrix as the form of Co(II)N bonds. For the selective oxidation of cyclohexane, Co-doping can markedly promote the catalytic performance of g-C3N4 catalyst due to the synergistic effect of Co species and g-C3N4 hybrid. Furthermore, the content of Co largely affected the activity of Co-doped g-C3N4 catalysts, among which the catalyst with 9.0 wt% Co content exhibited the highest yield (9.0%) of cyclohexanone and cyclohexanol, as well as a high stability. Meanwhile, the reaction mechanism over Co-doped g-C3N4 catalysts was elaborated.
A host-guest approach to fabricate metallic cobalt nanoparticles embedded in silk-derived N-doped carbon fibers for efficient hydrogen evolution
Fenglei Lyu, Qingfa Wang, Han Zhu, Mingliang Du, Li Wang, Xiangwen Zhang
2017, 2(2): 151-159. doi: 10.1016/j.gee.2017.01.007
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Hydrogen evolution reaction (HER) plays a key role in generating clean and renewable energy. As the most effective HER electrocatalysts, Pt group catalysts suffer from severe problems such as high price and scarcity. It is highly desirable to design and synthesize sustainable HER electrocatalysts to replace the Pt group catalysts. Due to their low cost, high abundance and high activities, cobalt-incorporated N-doped nanocarbon hybrids are promising candidate electrocatalysts for HER. In this report, we demonstrated a robust and eco-friendly host-guest approach to fabricate metallic cobalt nanoparticles embedded in N-doped carbon fibers derived from natural silk fibers. Benefiting from the one-dimensional nanostructure, the well-dispersed metallic cobalt nanoparticles and the N-doped thin graphitized carbon layer coating, the best Co-based electrocatalyst manifests low overpotential (61 mV@10 mA/cm2) HER activity that is comparable with commercial 20% Pt/C, and good stability in acid. Our findings provide a novel and unique route to explore high-performance noble-metal-free HER electrocatalysts.
CoFe2O4/carbon nanotube aerogels as high performance anodes for lithium ion batteries
Xin Sun, Xiaoyi Zhu, Xianfeng Yang, Jin Sun, Yanzhi Xia, Dongjiang Yang
2017, 2(2): 160-167. doi: 10.1016/j.gee.2017.01.008
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High-performance lithium ion batteries (LIBs) require electrode material to have an ideal electrode construction which provides fast ion transport, short solid-state ion diffusion, large surface area, and high electric conductivity. Herein, highly porous three-dimensional (3D) aerogels composed of cobalt ferrite (CoFe2O4, CFO) nanoparticles (NPs) and carbon nanotubes (CNTs) are prepared using sustainable alginate as the precursor. The key feature of this work is that by using the characteristic egg-box structure of the alginate, metal cations such as Co2+ and Fe3+ can be easily chelated via an ion-exchange process, thus binary CFO are expected to be prepared. In the hybrid aerogels, CFO NPs interconnected by the CNTs are embedded in carbon aerogel matrix, forming the 3D network which can provide high surface area, buffer the volume expansion and offer efficient ion and electron transport pathways for achieving high performance LIBs. The as-prepared hybrid aerogels with the optimum CNT content (20 wt%) delivers excellent electrochemical properties, i.e., reversible capacity of 1033 mAh g−1 at 0.1 A g−1 and a high specific capacity of 874 mAh g−1 after 160 cycles at 1 A g−1. This work provides a facile and low cost route to fabricate high performance anodes for LIBs.
Insights into electrochemical CO2 reduction on tin oxides from first-principles calculations
Siwen Wang, Jiamin Wang, Hongliang Xin
2017, 2(2): 168-171. doi: 10.1016/j.gee.2017.02.005
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Density functional theory calculations were used to unravel the mechanism of CO2 electroreduction on SnO surfaces. Under highly reducing conditions (< −0.6 V vs. RHE), the SnO(101) surface with oxygen vacancies is likely the active phase for CO2 reduction. We showed that the proton-electron transfer to adsorbed *CO2 forming *OCHO, a key intermediate for producing HCOOH, is energetically more favorable than the formation of *COOH, justifying the selectivity trends observed on Sn-based electrocatalysts. With linear scaling relations, we propose the free formation energy of *CO2 at the oxygen vacancy as the reactivity descriptor. By engineering the strain of the SnO(101) surface, the selectivity towards HCOOH can be further optimized at reduced overpotentials.

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