Xiaoru Guo

Constructing 2D Porous Graphitic C3N4 Nanosheets/Nitrogen‐Doped Graphene/Layered MoS2 Ternary Nanojunction with Enhanced Photoelectrochemical Activity

A 2D porous graphitic C3 N4 nanosheets/nitrogen-doped graphene/layered MoS2 ternary nanojunction is synthesized using a simple pyrolysis process followed by a hydrothermal treatment. The 2D ternary nanojunction exhibits significantly enhanced photoelectrochemical and photocatalytic activities due to the large contact area, efficient light absorption, and rapid charge separation and transport.

Perpendicularly Oriented MoSe2/Graphene Nanosheets as Advanced Electrocatalysts for Hydrogen Evolution

By increasing the density of exposed active edges, the perpendicularly oriented structure of MoSe2 nanosheets facilitates ion/electrolyte transport at the electrode interface and minimizes the restacking of nanosheets, while the graphene improves the electrical contact between the catalyst and the electrode. This makes the MoSe2 /graphene hybrid perfect as a catalyst in the hydrogen evolution reaction (HER). It shows a greatly improved catalytic activity compared with bare MoSe2 nanosheets.

A 3D hybrid of layered MoS2/nitrogen-doped graphene nanosheet aerogels: an effective catalyst for hydrogen evolution in microbial electrolysis cells

Cost-effective catalysts are the key to the successful deployment of microbial electrolysis cells (MECs) for hydrogen production from organic wastes. Herein, we report a novel catalyst for hydrogen evolution in MECs based on a 3D hybrid of layered MoS2/nitrogen-doped graphene nanosheet aerogels (3D MoS2/N-GAs) that were prepared by a facile hydrothermal approach. A high output current density of 0.36 mA cm−2 with a hydrogen production rate of 0.19 m3 H2 m−3 d−1 was achieved for the hybrid at a 0.8 V bias, significantly higher than that of MoS2 nanosheets and N-GAs alone and comparable to that of the Pt/C catalyst when being applied in MECs. The outstanding performance of the hybrid benefits from its 3D conductive networks, porous structure, and strong synergic effects between MoS2 nanosheets and N-GAs, making it a promising catalyst for hydrogen production from wastewater through bio-electrochemical reactions.

Strongly Coupled 3D Hybrids of N‐doped Porous Carbon Nanosheet/CoNi Alloy‐Encapsulated Carbon Nanotubes for Enhanced Electrocatalysis

A novel 3D nanoarchitecture comprising in situ-formed N-doped CoNi alloy-encapsulated carbon nanotubes (CoNi-NCNTs) grown on N-doped porous carbon nanosheets (NPCNs) is designed and constructed for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). When evaluated as an electrocatalyst for ORR, the hybrid shows efficient catalytic activity, high selectivity, superior durability, and strong tolerance against methanol crossover compared with the commercial Pt/C catalyst. Such good oxygen reduction reaction performance is comparable to most of the previously reported results and the synergistic effect is found to boost the catalytic performance. Moreover, the constructed hybrid exhibits an excellent ORR activity with a current density of 10 mA cm(-2) at 1.59 V and an onset potential of 1.57 V, even beyond the state-of-the-art Ir/C catalyst in alkaline media. The enhancement in electrochemical performance can be attributed to the unique morphology and defect structures, high porosity, good conductive networks, and strongly interacting CoNi-NCNT and NPCN in the hybrid. These results suggest the possibility for the development of effective nanocarbon electrocatalysts to replace commercial noble metal catalysts for direct use in fuel cells and water splitting devices.

Controllable Synthesis and Tunable Photocatalytic Properties of Ti3+-doped TiO2

Photocatalysts show great potential in environmental remediation and water splitting using either artificial or natural light. Titanium dioxide (TiO2)-based photocatalysts are studied most frequently because they are stable, non-toxic, readily available, and highly efficient. However, the relatively wide band gap of TiO2 significantly limits its use under visible light or solar light. We herein report a facile route for controllable synthesis of Ti3+-doped TiO2 with tunable photocatalytic properties using a hydrothermal method with varying amounts of reductant, i.e., sodium borohydride (NaBH4). The resulting TiO2 showed color changes from light yellow, light grey, to dark grey with the increasing amount of NaBH4. The present method can controllably and effectively reduce Ti4+ on the surface of TiO2 and induce partial transformation of anatase TiO2 to rutile TiO2, with the evolution of nanoparticles into hierarchical structures attributable to a high pressure and strong alkali environment in the synthesis atmosphere; in this way, the photocatalytic activity of Ti3+-doped TiO2 under visible-light can be tuned. The as-developed strategy may open up a new avenue for designing and functionalizing TiO2 materials for enhancing visible light absorption, narrowing band gap, and improving photocatalytic activity.

Porous Carbon Nanosheets Codoped with Nitrogen and Sulfur for Oxygen Reduction Reaction in Microbial Fuel Cells

In this work, a simple synthesis strategy has been developed for the preparation of nitrogen- and sulfur-codoped porous carbon nanosheets (N/S-CNS) as a cathode catalyst for microbial fuel cells (MFCs). The as-prepared N/S-CNS showed favorable features for electrochemical energy conversion such as high surface area (1004 m(2) g(-1)), defect structure, and abundant exposure of active sites that arose primarily from porous nanosheet morphology. Benefiting from the unique nanostructure, the resulting nanosheets exhibited effective electrocatalytic activity toward oxygen reduction reaction (ORR). The onset potential of the N/S-CNS in linear-sweep voltammetry was approximately -0.05 V vs Ag/AgCl in neutral phosphate buffer saline. Electrochemical impedance spectroscopy showed that the ohmic and charge-transfer resistance of the codoped catalyst were 1.5 and 14.8 Ω, respectively, both of which were lower than that of platinum/carbon (Pt/C). Furthermore, the electron-transfer number of the N/S-CNS was calculated to be ∼3.5, suggesting that ORR on the catalyst proceeds predominantly through the favorable four-electron pathway. The MFC with N/S-CNS as a cathode catalyst generated current density (6.6 A m(-2)) comparable to that with Pt/C (7.3 A m(-2)). The high durability and low price indicate that N/S-CNS can be a competitive catalyst for applications of MFCs.

Novel Hybrid Carbon Nanofiber/Highly Branched Graphene Nanosheet for Anode Materials in Lithium-Ion Batteries

The novel hybrid carbon nanofiber (CNF)/highly branched graphene nanosheet (HBGN) is synthesized via a simple two-step CVD method and its application as the anode material in a lithium-ion battery (LIB) is demonstrated. The CNFs offer a good electrical conductivity and a robust supporting structure, while the HBGNs provide increased Li storage sites including nanoporous cavities, large surface area, and edges of exposed graphene platelets. The hybrid material showed a reversible capacity of 300 mAh g(-1) with excellent cycling stability. Our study provides a new avenue for design and synthesis of carbon-carbon hybrid materials for versatile applications.

A room-temperature liquid metal-based self-healing anode for lithium-ion batteries with an ultra-long cycle life

Benefiting from fluidity and surface tension, materials in a liquid form are one of the best candidates for self-healing applications. This feature is highly desirable for improving the life cycle of lithium-ion batteries (LIBs) because the volume expansion/contraction during the cycles of high-capacity anodes such as Si and Sn can result in mechanical fracture and lead to inferior cycle performance. Here, we report a novel room-temperature liquid metal (LM) as the anode to improve the cycle life of LIBs. The LM anode comprises an alloy of Sn and Ga, a liquid at room temperature with inherent self-healing properties, as confirmed by the in situ and ex situ analyses. Because both Ga and Sn have high theoretical capacities (769 and 990 mA h g−1, respectively), the resulting LM anode delivers a high capacity of 775, 690, and 613 mA h g−1 at the rate of 200, 500, and 1000 mA g−1, respectively. There was no obvious decay in more than 4000 cycles with a capacity of ∼400 mA h g−1 at 4000 mA g−1, realizing the best cycle performance among all metal anodes.

Novel hybrid Si film/carbon nanofibers as anode materials in lithium-ion batteries

The hybrid Si film/carbon nanofiber (CNF) as an anode in lithium-ion batteries (LIBs) was synthesized using a two-step chemical vapour deposition (CVD) method. This binder- and conductive additive-free electrode delivered a discharge capacity of 1000 mA h g−1 over 200 cycles. CNFs as a support material were directly grown on a stainless steel foil, while the stress-resilient Si films coated on the CNFs offered high Li storage capacity.

Graphene-Based Materials for Photoanodes in Dye-Sensitized Solar Cells

This article reviews the research on the use of graphene and related materials in the photoanode of dye-sensitized solar cells (DSSCs). Graphene-based materials, such as pristine graphene, graphene oxide, and reduced graphene oxide, have properties attractive for various components of the DSSC photoanode. We first provide a brief introduction to graphene properties and analyze requirements for making a high-performance photoanode. Then we introduce applications of graphene-based materials in each part of the DSSC photoanode, i.e., the transparent conducting electrode, the sensitizing material, and the semiconducting layer. Particularly, we discuss how the incorporation of graphene-based materials in those components can enhance the photoanode performance. It is clear that the outstanding properties of graphene, such as the fast electron transfer ability, high Young’s modulus, and good transparency, benefit DSSC photoanode research, and doping or surface modifications of graphene nanosheets with other materials can also improve the photoanode and thus the resulting cell performance. Finally, we present an outlook for current issues and further trends for using graphene materials in DSSC photoanodes.