Mesoporous TiO2 has gained increasing interest because of its outstanding properties and promising applications in a wide range of fields. Herein, we report the facile synthesis of ordered mesoporous black TiO2 (OMBT) materials, which exhibit excellent photocatalytic hydrogen evolution performances. In this case, the employment of a thermally stable and high-surface-area mesoporous TiO2 as the hydrogenation precursor is the key for fabricating the OMBT materials, which not only facilitate H2 gas diffusion into TiO2 and interaction with their structures but also maintain the ordered mesoporous structures as well as inhibit the phase transformation (from anatase to rutile) and crystal growth during hydrogenation at 500 °C. The resultant OMBT materials possess a relatively high surface area of ∼124 m(2) g(-1) and a large pore size and pore volume of ∼9.6 nm and 0.24 cm(3) g(-1), respectively. More importantly, the OMBT materials can extend the photoresponse from ultraviolet to visible and infrared light regions and exhibit a high solar-driven hydrogen production rate (136.2 μmol h(-1)), which is almost two times as high as that of pristine mesoporous TiO2 (76.6 μmol h(-1)).

Polymeric carbon nitride (C3N4) has emerged as the most promising candidate for metal-free photocatalysts but is plagued by low activity due to the poor quantum efficiency and low specific surface area. Exfoliation of bulk crystals into ultrathin nanosheets has proven to be an effective and widely used strategy for enabling high photocatalytic performances; however, this process is complicated, time-consuming, and costly. Here, we report a simple bottom-up method to synthesize porous few-layer C3N4, which involves molecule self-assembly into layered precursors, alcohol molecules intercalation, and subsequent thermal-induced exfoliation and polycondensation. The as-prepared few-layer C3N4 expose more active sites and greatly enhance the separation of charge carriers, thus exhibiting a 26-fold higher hydrogen evolution activity than bulk counterpart. Furthermore, we find that both the high activity and selectivity for the oxidative coupling of amines to imines can be obtained under visible light that surpass those of other metal-free photocatalysts so far.

Nitrogen-doped graphene nanosheets (NGS) with the nitrogen level as high as 10.13 atom% were synthesized via a simple hydrothermal reaction of graphene oxide (GO) and urea. N-doping and reduction of GO were achieved simultaneously under the hydrothermal reaction. In the fabrication, the nitrogen-enriched urea plays a pivotal role in forming the NGS with a high nitrogen level. During the hydrothermal process, the N-dopant of urea could release NH 3 in a sustained manner, accompanied by the released NH 3 reacting with the oxygen functional groups of the GO and then the nitrogen atoms doped into graphene skeleton, leading to the formation of NGS. The nitrogen level and species could be conveniently controlled by easily tuning the experimental parameters, including the mass ratio between urea and GO and the hydrothermal temperature. Remarkably, in 6 M KOH electrolyte, the synthesized NGS with both high nitrogen (10.13 atom%) and large surface area (593 m 2 g 21 ) exhibits excellent capacitive behaviors (326 F g 21 , 0.2 A g 21 ), superior cycling stability (maintaining initial capacity even) and coulombic efficiency (99.58%) after 2000 cycles. The energy density of 25.02 Wh kg 21 could be achieved at power density of 7980 W kg 21 by a two-electrode symmetric capacitor test. A series of experiments results demonstrated that not only the N-content but also the N-type are very significant for the capacitive behaviors. In more detail, the pyridinic-N and pyrrolic-N play mainly roles for improving pseudo-capacitance by the redox reaction, while quaternary-N could enhance the conductivity of the materials which is favorable to the transport of electrons during the charge/discharge process. Hence, the approach in this work could provide a new way for preparing NGS materials which could be used as advanced electrodes in high performance supercapacitors.

Simultaneous highly efficient production of hydrogen and conversion of biomass into value‐added products is meaningful but challenging. Herein, a porous nanospindle composed of carbon‐encapsulated MoO2‐FeP heterojunction (MoO2‐FeP@C) is proposed as a robust bifunctional electrocatalyst for hydrogen evolution reaction (HER) and biomass electrooxidation reaction (BEOR). X‐ray photoelectron spectroscopy analysis and theoretical calculations confirm the electron transfer from MoO2 to FeP at the interfaces, where electron accumulation on FeP favors the optimization of H2O and H* absorption energies for HER, whereas hole accumulation on MoO2 is responsible for improving the BEOR activity. Thanks to its interfacial electronic structure, MoO2‐FeP@C exhibits excellent HER activity with an overpotential of 103 mV at 10 mA cm−2 and a Tafel slope of 48 mV dec−1. Meanwhile, when 5‐hydroxymethylfurfural is chosen as the biomass for BEOR, the conversion is almost 100%, and 2,5‐furandicarboxylic acid (FDCA) is obtained with the selectivity of 98.6%. The electrolyzer employing MoO2‐FeP@C for cathodic H2 and anodic FDCA production requires only a low voltage of 1.486 V at 10 mA cm−2 and can be powered by a solar cell (output voltage: 1.45 V). Additionally, other BEORs coupled with HER catalyzed by MoO2‐FeP@C also have excellent catalytic performance, implying their good versatility.

An in situ catalytic etching strategy is developed to fabricate holey reduced graphene oxide along with simultaneous coupling with a small-sized Mo N-Mo C heterojunction (Mo N-Mo C/HGr). The method includes the first immobilization of H PMo O (PMo ) clusters on graphite oxide (GO), followed by calcination in air and NH to form Mo N-Mo C/HGr. PMo not only acts as the Mo heterojunction source, but also provides the Mo species that can in situ catalyze the decomposition of adjacent reduced GO to form HGr, while the released gas (CO) and introduced NH simultaneously react with the Mo species to form an Mo N-Mo C heterojunction on HGr. The hybrid exhibits superior activity towards the hydrogen evolution reaction with low onset potentials of 11 mV (0.5 m H SO ) and 18 mV (1 m KOH) as well as remarkable stability. The activity in alkaline media is also superior to Pt/C at large current densities (>88 mA cm ). The good activity of Mo N-Mo C/HGr is ascribed to its small size, the heterojunction of Mo N-Mo C, and the good charge/mass-transfer ability of HGr, as supported by a series of experiments and theoretical calculations.

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been devoted to various energy storage and conversion systems. [1,2] Metal-air batteries, especially Zn-air batteries (ZABs) have been regarded as a promising energy storage system due to their low-cost, high theoretical specific energy density (1084 Wh kg −1 ), and environmental friendliness. [3][4][5] Nevertheless, the multistep and proton-coupled electron transfer processes of the reversible oxygen reactions lead to sluggish kinetics for oxygen reduction (ORR) and oxygen evolution (OER) at aircathode, which are the bottlenecks of inefficient and unideal lifetime. [6] The current benchmark catalysts for simply ORR or OER are precious-metal-based catalysts (Pt, Ir, RuO 2 , etc.), but their high cost, supply scarcity, and poor bifunctional catalytic characters have greatly restricted their applications in ZABs. [7,8] In response, various transition-based catalysts with high activity and good durability have been explored, such as transition metal oxides, chalcogenides, and metal-heteroatom doped carbon materials. [9][10][11][12][13][14] Despite significant progress, current bifunctional catalysts are still facing the problems of insufficient activity and stability together with poor mass transport properties.Alternatively, metal-nitrogen-carbon (M-N-C) systems comprising the earth abundant transition metals and catalytic active metalN x centers with carbonized ligand have received growing interest due to their low cost and excellent catalytic activities. [15][16][17] Specially, Co-N-C has emerged as ORR catalyst for improvement the overall performance of ZABs. [18,19] Inspired by the excellent OER performance of Co-based catalysts (e.g., cobalt metal and cobalt oxide) and intrinsically electrical conductivity of Co metal, [20,21] so constructing hierarchical structure of Co-N-C contained Co metal maybe an effective way to promote the bifunctional ORR/OER activity. At present, various strategies have been applied to synthesize Co-N-C structures. Traditionally, carbonized the Co-based precursors (such as porphyrins and phthalocyanines) have been developed for several decades to synthesize metal contained N-doped carbon nanostructures, [22,23] but always suffer from large nanoparticles size and ununiformed structures. Hence, much efforts have been devoted to construct Co-N-C-based catalysts with novel morphology and structures, such as core-shell or single-atom dispersed Co-N-C catalysts combined with carbon nanotubes Developing non-precious-metal bifunctional oxygen reduction and evolution reaction (ORR/OER) catalysts is a major task for promoting the reaction efficiency of Zn-air batteries. Co-based catalysts have been regarded as promising ORR and OER catalysts owing to the multivalence characteristic of cobalt element. Herein, the synthesis of Co nanoislands rooted on Co-N-C nanosheets supported by carbon felts (Co/Co-N-C) is reported. Co nanosheets rooted on the carbon felt derived from electrodeposition are applied as the self-template and cobalt source. The synergistic effect of metal Co islands with OER a...

Oxygen lone-pairs (|O) are responsible for the extra-capacity observed in Li-rich Li2MO3 electrodes and not in LiMO2. M–O covalency is required to stabilize the oxidized O− species involved in the anionic process and to prevent O2 release.