Yang Hou

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.

High-performance bi-functional electrocatalysts of 3D crumpled graphene–cobalt oxide nanohybrids for oxygen reduction and evolution reactions

We report a high-performance bi-functional electrocatalyst composed of 3D crumpled graphene (CG)–cobalt oxide nanohybrids. This is the first report on using CG coupled with nanocrystals as both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts. The nitrogen-doped CG–CoO hybrid exhibits excellent catalytic activity and durability, making it a high-performance non-precious metal-based bi-functional catalyst for both ORR and OER.

Vertically oriented cobalt selenide/NiFe layered-double-hydroxide nanosheets supported on exfoliated graphene foil: an efficient 3D electrode for overall water splitting

Developing cost-effective electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in basic media is critical to renewable energy conversion technologies. Here, we report a ternary hybrid that is constructed by in situ growth of cobalt selenide (Co0.85Se) nanosheets vertically oriented on electrochemically exfoliated graphene foil, with subsequent deposition of NiFe layered-double-hydroxide by a hydrothermal treatment. The resulting 3D hierarchical hybrid, possessing a high surface area of 156 m2 g−1 and strong coupling effect, exhibits excellent catalytic activity for OER, which only requires overpotentials of 1.50 and 1.51 V to attain current densities of 150 and 250 mA cm−2, respectively. These overpotentials are much lower than those reported for other non-noble-metal materials and Ir/C catalysts. The hybrid also efficiently catalyzes HER in base with a current density of 10 mA cm−2 at an overpotential of −0.26 V. Most importantly, we achieve a current density of 20 mA cm−2 at 1.71 V by using the 3D hybrid as both a cathode and an anode for overall water splitting, which is well comparable to the integrated performance of Pt/C and Ir/C catalysts.

Strongly Coupled Ternary Hybrid Aerogels of N-deficient Porous Graphitic-C3N4 Nanosheets/N-Doped Graphene/NiFe-Layered Double Hydroxide for Solar-Driven Photoelectrochemical Water Oxidation

Developing photoanodes with efficient sunlight harvesting, excellent charge separation and transfer, and fast surface reaction kinetics remains a key challenge in photoelectrochemical water splitting devices. Here we report a new strongly coupled ternary hybrid aerogel that is designed and constructed by in situ assembly of N-deficient porous carbon nitride nanosheets and NiFe-layered double hydroxide into a 3D N-doped graphene framework architecture using a facile hydrothermal method. Such a 3D hierarchical structure combines several advantageous features, including effective light-trapping, multidimensional electron transport pathways, short charge transport time and distance, strong coupling effect, and improved surface reaction kinetics. Benefiting from the desirable nanostructure, the ternary hybrid aerogels exhibited remarkable photoelectrochemical performance for water oxidation. Results included a record-high photocurrent density that reached 162.3 μA cm(-2) at 1.4 V versus the reversible hydrogen electrode with a maximum incident photon-to-current efficiency of 2.5% at 350 nm under AM 1.5G irradiation, and remarkable photostability. The work represents a significant step toward the development of novel 3D aerogel-based photoanodes for solar water splitting.

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.

Wafer-sized multifunctional polyimine-based two-dimensional conjugated polymers with high mechanical stiffness

One of the key challenges in two-dimensional (2D) materials is to go beyond graphene, a prototype 2D polymer (2DP), and to synthesize its organic analogues with structural control at the atomic- or molecular-level. Here we show the successful preparation of porphyrin-containing monolayer and multilayer 2DPs through Schiff-base polycondensation reaction at an air–water and liquid–liquid interface, respectively. Both the monolayer and multilayer 2DPs have crystalline structures as indicated by selected area electron diffraction. The monolayer 2DP has a thickness of∼0.7u2009nm with a lateral size of 4-inch wafer, and it has a Youngs modulus of 267±30u2009GPa. Notably, the monolayer 2DP functions as an active semiconducting layer in a thin film transistor, while the multilayer 2DP from cobalt-porphyrin monomer efficiently catalyses hydrogen generation from water. This work presents an advance in the synthesis of novel 2D materials for electronics and energy-related applications.

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.

Ultrasensitive Chemical Sensing through Facile Tuning Defects and Functional Groups in Reduced Graphene Oxide

Herein, we report on a facile, low-cost, and efficient method to tune the structure and properties of chemically reduced graphene oxide (rGO) by applying a transient voltage across the rGO for ultrasensitive gas sensors. A large number of defects, including pits, are formed in the rGO upon the voltage activation. More interestingly, the number of epoxide and ether functional groups in the rGO increased after the voltage activation. The voltage-activated rGO was highly sensitive to NO2 with a sensitivity 500% higher than that of the original rGO. The lower detection limit can reach an unprecedented ultralow concentration of 50 ppb for NO2 sensing. Density functional theory (DFT) calculations revealed that the high sensitivity to NO2 is attributed to the efficient charge transfer from ether groups to NO2, which is the dominant sensing mechanism. This study points to a promising method to tune the properties of graphene-based materials through the creation of additional defects and functional groups for high-performance gas sensors.