The development of highly active and stable earth-abundant electrocatalysts to reduce or eliminate the reliance on noble-metal based ones for hydrogen evolution reaction (HER) over a broad pH range remains a great challenge. Herein, hierarchical porous Co9S8/N-doped carbon@MoS2 (Co9S8/NC@MoS2) polyhedrons have been synthesized by a facile hydrothermal approach using highly conductive Co/NC polyhedrons composed of cobalt nanoparticles embedded in N-doped carbon matrices as both the structural support and cobalt source. The Co/NC polyhedrons were prepared by direct carbonization of Co-based zeolitic imidazolate framework (ZIF-67) in Ar atmosphere. Benefiting from the prominent synergistic effect of N-doped carbon enhancing the conductivity of the hybrid, MoS2 and Co9S8 providing abundant catalytically active sites as well as the well-defined polyhedral structure promoting mechanical stability, the as-synthesized Co9S8/NC@MoS2 shows excellent HER activity and good stability over a broad pH range, with onset overpotentials of 4, 38, and 45 mV, Tafel slopes of 60.3, 68.8, and 126.1 mV dec–1, and overpotentials of 67, 117, and 261 mV at 10 mA cm–2 in 1.0 M KOH, 0.5 M H2SO4, and 1.0 M phosphate buffer solution (PBS), respectively. This work provides a general and promising approach for the design and synthesis of inexpensive and efficient pH-universal HER electrocatalysts.Keywords: Co9S8/N-doped carbon@MoS2; electrocatalysts; hydrogen evolution reaction; polyhedrons; synergistic effect; zeolitic imidazolate framework;

This study was mainly aimed at designing molecular p–n heterojunctions on the surface of N-doped TiO2 for visible-light hydrogen evolution. A series of NiO/N-TiO2 samples were prepared via NH3-postnitridation of nickel oxide-modified TiO2. H2 production from ethanol/water solution was utilized as a model reaction to evaluate the photocatalytic properties of the catalysts. Compared to N-TiO2, a 90-fold-enhanced H2 evolution rate was achieved over the optimal NiO/N-TiO2 catalyst with a 0.5 wt% Ni content. Detailed characterizations clearly showed that loading NiO via wet impregnation leads to high dispersion of Ni2+ species on the surface oxygen vacancy (Vo) sites of the anatase TiO2 nanoparticles, predominantly presenting mononuclear Ti–O–Ni heteroatomic clusters on the surface of TiO2 in the case of low Ni content. These surface heteroatomic clusters can speed up the transfer and separation of photogenerated carriers of N-TiO2. It can thus be established that the molecular Ti–O–Ni heterojunctions are the main contributors to the synergistic enhancement of H2 evolution, whereas NiO nanoclusters are not responsible for the photoactivity. Only one of the N species, N–Ti–Vo, was active and effective for this cooperation with the hydrogen-releasing Ni sites, which can induce ca. 20-fold improvement of hydrogen production over NiO/TiO2 under visible light irradiation.

A macroporous SiO2 (Macro-SiO2), which has uniformed macropores, an open-framework structure, and thin walls, was synthesized to support Ziegler–Natta catalysts. The immobilization behaviors of the Ziegler–Natta catalysts inside the Macro-SiO2 were investigated. Notable agglomerations of δ-MgCl2/titanium complex were observed because of the unconstrained environment of the Macro-SiO2. A highly superficial Ti content and a heterogeneously chemical structure of Ti active sites were thus achieved inside the Macro-SiO2. The ethylene polymerization results revealed that the Macro-SiO2/MgCl2/TiCl4 exhibited much higher catalytic activity (i.e., 12.1 × 106 g PE·(mol Ti·h)−1 or 17.8 × kg PE·(g cat·h)−1) than that of the traditional 955-SiO2 supported catalyst (i.e., 2.0 × 106 g PE·(mol Ti·h)−1 or 2.7 × kg PE·(g cat·h)−1). Finally, the fragmentation behavior of Macro-SiO2/MgCl2/TiCl4 was investigated during the polymerization. This unconstrained environment of Macro-SiO2 afforded fewer resistances to the diffusion of reactants and also the polymer growth.

Tubular-structured nanomaterials with tailorable crystal structures and shell architectures whose properties can be tuned without changing their chemical compositions are attractive in electrochemical energy conversion and storage fields. Herein, we report the fabrication of tubular-structured orthorhombic CoSe2 (o-CoSe2) and cubic CoSe2 (c-CoSe2) by calcining monoclinic Co3Se4 nanotubes (Co3Se4 NTs) prepared by a facile precursor transformation method. Benefiting from advantageous structural features, including functional shells and well-defined interior voids, the tubular-structured o-CoSe2 showed a high power conversion efficiency of 9.34% as a counter electrode catalyst for dye-sensitized solar cells (DSSCs), superior to that of a Pt counter electrode (8.15%), under AM 1.5 G irradiation. In addition, the o-CoSe2 nanotubes also demonstrated excellent electrocatalytic activity in terms of low onset overpotential (∼54 mV) and small Tafel slope (∼65.9 mV per decade) as a hydrogen evolution reaction (HER) catalyst in alkaline medium. Hence, this work provides a promising strategy to selectively design and synthesize highly active electrocatalysts for energy conversion.

•AlCl3.6H2O aqueous solution was used as the solvent for chitosan.•The chitosan/poly(acrylic amide-acrylic acid) hybrid double network hydrogels were prepared.•The physical crosslinking network was formed by the incorporation of Al3+ ion.•The chitosan/poly(acrylic amide-acrylic acid) hydrogel could show the tensile strength of 0.54 MPa and elongation at break of 2203.7%.Development of bio-based hydrogels with good mechanical properties is of great importance for their excellent biocompatibility and biodegradability. In this paper, chitosan (CS) based double network (DN) hydrogel was prepared by dissolving CS in AlCl3·6H2O aqueous solution instead of acetic acid solution. After dissolving acrylic amide (AM), acrylic acid (AA), N, N’-methylenebisacrylamide and 2-hydroxy-4′-(2-hydoxyethoxy)-2-methylpropiophenone were added into the CS/Al3+ solution and the CS/PAMAA-Al3+ DN hydrogel was prepared by UV polymerization. The hybrid physical and chemical crosslinked network hydrogels were prepared. The tensile and compression properties of CS/PAMAA-Al3+ DN hydrogel were studied. The results showed that the CS/PAMAA-Al3+ DN hydrogels have high toughness, stretch-ability, and excellent shape recovery properties. The CS/PAMAA-Al3+ DN hydrogel could show the tensile strength of 0.54 MPa and elongation at break of 2203.7%. These properties arise from the dynamic ionic interaction between Al3+ and CS/PAMAA macromolecular chains.

•Four indeno[1,2-b]indole-based new organic dyes have been synthesized.•These dyes were designed into a D–π–A structure and applied in DSSCs.•Different acceptors were used to tune the photoelectric properties of the dyes.•A highest PCE of 6.29% was achieved by the dye with a cyanoacrylic acid acceptor.Four new metal-free organic dyes QX15–18 based on indeno[1,2-b]indole have been successfully designed and synthesized. These D–π–A type dyes consist of an indeno[1,2-b]indole donor and a benzene or thiophene π-bridge. In an attempt to tune their photoelectric properties, the effects of different acceptor groups including cyanoacrylic acid, rhodanine-3-acetic acid, and 2-(1,1-dicyanomethylene)rhodanine (DCRD) have been investigated. The dye QX15 with a cyanoacrylic acid acceptor exhibited a highest Voc of 813 mV and a high Jsc of 11.0 mA cm−2, generating a highest power conversion efficiency of 6.29%. Meanwhile, the dye QX18 with a DCRD acceptor and a thiophene π-bridge showed a significantly improved Jsc of 11.9 mA cm−2, which could be attributed to its red-shifted absorption spectra and high molar absorption coefficient.Download high-res image (170KB)Download full-size image

•Novel Co-Fe-Se/S porous nanocubes (PNCs) were prepared by a template method.•The PNCs were applied as efficient CE electrocatalysts for DSSCs.•The PNCs had large surface area, high catalytic activity and good conductivity.•The PCEs (9.58% and 9.06%) of the PNCs were higher than that of Pt (8.16%).A novel series of ternary compounds, namely cobalt iron selenide/sulfide nanocubes, are successfully synthesized as counter electrode (CE) materials for dye-sensitized solar cells (DSSCs), which deliver excellent performances. Homogeneous cobalt iron Prussian-blue-analog (PBA) nanocubes are prepared as the templates and are subsequently dealt with selenation/sulfidation processes via hydrothermal methods. Owing to their unique morphology, porous structure, high surface area, small charge transfer resistance and high diffusion coefficient, the Co-Fe-Se/S nanocubes possess high catalytic activity and excellent conductivity, which are tested and verified by electrochemical measurements. Meanwhile, cobalt iron selenide/sulfide nanocubes CEs achieve high efficiencies of 9.58% and 9.06%, respectively, which are both higher than that of Pt CE (8.16%). All these prominent merits make them outstanding and promising participants among Pt-free CE materials of DSSCs with lower production costs and higher power conversion efficiency.Download high-res image (308KB)Download full-size image

•Ternary Ni-Co-Se alloy based hollow microspheres were successfully synthesized.•Different hydrothermal temperatures led to different hollow morphologies.•The prepared Ni-Co-Se alloy based CEs all showed good catalytic activities.•Ni-Co-Se-180 CE showed a PCE of 9.04% which was much higher than Pt CE (8.07%).Ternary nickel cobalt selenide (Ni-Co-Se) alloy based hollow microspheres have been successfully synthesized via a simple one-step hydrothermal route by controlling different hydrothermal temperatures. The prepared samples were divided by reaction temperatures (140, 160, 180 and 200 °C) and named as Ni-Co-Se-140, Ni-Co-Se-160, Ni-Co-Se-180 and Ni-Co-Se-200, respectively. With the temperature increasing, the hollow microspheres formed at the lower temperature and broke at the higher temperature, and the sample Ni-Co-Se-180 exhibited the most regular and homogeneous hollow microspheres with a size of 1.5–2.5 μm. Moreover, the Ni atomic ratios in Ni-Co-Se alloys increased with the temperature rising. The prepared Ni-Co-Se alloys were used as counter electrode (CE) catalysts for dye-sensitized solar cells (DSSCs). A series of electrochemical tests all verified Ni-Co-Se alloy based CEs had superior electrocatalytic activities and Ni-Co-Se-180 CE displayed the largest current density, lowest overpotential and smallest charge-transfer resistance than the other CEs and Pt CEs. Benefiting from their unique morphologies and surface structures, the cells with the Ni-Co-Se-160, Ni-Co-Se-180 and Ni-Co-Se-200 based CEs achieved high efficiencies of 8.39%, 9.04% and 8.72%, respectively, which were all higher than that of Pt CE (8.07%).Download high-res image (88KB)Download full-size image

In this work, morphology-tuned ternary nickel cobalt selenides based on different Ni/Co molar ratios have been synthesized via a simple precursor conversion method and used as counter electrode (CE) materials for dye-sensitized solar cells (DSSCs). The experimental facts and mechanism analysis clarified the possible growth process of product. It can be found that the electrochemical performance and structures of ternary nickel cobalt selenides can be optimized by tuning the Ni/Co molar ratio. Benefiting from the unique morphology and tunable composition, among the as-prepared metal selenides, the electrochemical measurements showed that the ternary nickel cobalt selenides exhibited a more superior electrocatalytic activity in comparison with binary Ni and Co selenides. In particular, the three-dimensional dandelion-like Ni0.33Co0.67Se microspheres delivered much higher power conversion efficiency (9.01%) than that of Pt catalyst (8.30%) under AM 1.5G irradiation.Keywords: counter electrode; dandelion-like structure; dye-sensitized solar cells; electrocatalytic activity; nickel cobalt selenides

•Four novel indolo[3,2-b]carbazole-based organic dyes have been synthesized.•These dyes are designed as a multi-donor–π–acceptor type.•The secondary donors led to striking changes of the photoelectronic properties.•QX02 with diethylaniline as the secondary donor achieved a PCE of 8.09%.Four novel indolo[3,2-b]carbazole-based multi-donor–π–acceptor type organic dyes QX01–04 have been designed, synthesized, and applied for dye-sensitized solar cells. These dyes consist of an indolo[3,2-b]carbazole core acting as the main donor group, a couple of groups such as ethylbenzene, N,N-diethylaniline, ethyloxylbenzene, and octyloxylbenzene acting as the secondary donors. The photophysical, electrochemical, and theoretical studies indicate that the four dyes are all capable as the photosensitizers. When introducing N,N-diethylaniline as the secondary donor, QX02 exhibits a broader absorption region and significantly improved IPCE values, which ensured a good light-harvesting ability and a high Jsc of 15.2 mA cm−2. Finally, QX02-based cell achieved a high efficiency of 8.09% which is very close to that of the commercial N719-based cell (8.26%) under 100 mW cm−2 irradiation.

•Four dyes QX05–08 based on indoloquinoxaline/phenothiazine were synthesized.•The dyes QX07 and QX08 were constructed as a D–D–π–A type structure.•The two dyes QX07 and QX08 showed excellent photoelectric properties.•A high PCE of 8.28% was achieved by QX07 with a thiophene π-bridge.Four metal-free organic dyes QX05–08 based on indoloquinoxaline and phenothiazine have been successfully designed and synthesized for dye-sensitized solar cells. The D–D–π–A type dyes QX07 and QX08 consist of an indoloquinoxaline donor, a phenothiazine donor, a cyanoacrylic acid acceptor/anchoring group and a thiophene or furan π-bridge. Other simple D–π–A type dyes QX05 and QX06 based on indoloquinoxaline and phenothiazine respectively have also been synthesized for comparison. The D–D–π–A type dyes QX07 and QX08 present good balanced structures and show excellent photoelectric properties. Especially, the dye QX07 with a thiophene unit as the π-bridge exhibits the best photovoltaic performances in solar cells. A high power conversion efficiency up to 8.28% with a Jsc of 15.3 mA cm−2 and a Voc of 757 mV have been achieved by the dye QX07 using an iodine electrolyte under standard conditions.

•Four samples CoMoS4, NiMoS4, CoMoS4-H and NiMoS4-H have been synthesized.•These composites were used as efficient HER electrocatalysts in a wide pH range.•CoMoS4-H and NiMoS4-H show low onset overpotentials of 8 mV and 26 mV in 1 M KOH.•The two also exhibited low onset overpotentials (83 mV and 160 mV) in 0.5 M H2SO4.Highly efficient and low-cost electrocatalysts are essential for producing hydrogen through water electrolysis. Here ternary compounds CoMoS4 and NiMoS4 were synthesized by a one-step reaction, and further CoMoS4-H and NiMoS4-H were obtained by heating the above two samples under Ar atmosphere. The above four materials both show uniformly small irregular nanoparticles. Each element of the four materials exhibits semblable valence without distinct difference of which S was −2, Mo was +6, Ni and Co were +2. We firstly use the above ternary materials as advanced electrocatalysts for HER over a wide pH range, of which CoMoS4-H displays the best performance with a low onset overpotential at 8 mV in 1.0 M KOH and 83 mV in 0.5 M H2SO4. NiMoS4-H also shows excellent performance with a low onset overpotential at 26 mV in 1.0 M KOH and 160 mV in 0.5 M H2SO4. In 1 M phosphate buffer solution, CoMoS4-H and NiMoS4-H exhibit onset overpotential at overpotential of 122 mV and 152 mV, respectively. These results indicate that the combination of earth-abundant sulfur, cobalt (or nickel) and molybdenum elements can provide highly active electrocatalysts for HER over a wide pH range.

•Novel triindole-modified porphyrin dyes were synthesized for the first time.•The push–pull type structure is favorable for charge transfer.•The dye with cyanoacylic acid as the acceptor exhibited better performances.•A power conversion efficiency up to 6.65% has been achieved.Two novel push–pull type Zn(II) porphyrin dyes (QX09 and QX10) have been synthesized for dye-sensitized solar cells (DSSCs). The two porphyrin dyes consist of the same porphyrin core with a triindole unit directly attached in its meso-position and different acceptor/anchoring groups carboxylic acid (for QX09) and cyanoacylic acid (for QX10) have been investigated. The photophysical, electrochemical and theoretical studies indicated that the two porphyrin dyes were both suitable as the photosensitizers. The dye QX10 exhibited a broader absorption region and significantly improved IPCE values compared with QX09, which ensured a better light-harvesting ability and a higher photocurrent. With the coadsorption of chenodeoxycholic acid (CDCA), the DSSCs based on the two dyes both obtained improved photovoltaic performances. Finally, QX10-based cell with CDCA achieved a high power conversion efficiency of 6.65% under AM 1.5G irradiation.

•The AlCl3·6H2O aqueous solution was used to dissolve chitosan.•The thermal degradation of chitosan and poly(vinyl alcohol) was suppressed in AlCl3·6H2O aqueous solution.•Glycerol had the positive effect on AlCl3·6H2O doped chitsosan/poly(vinyl alcohol) film.•The high performance chitosan/poly(vinyl alcohol) films were obtained with AlCl3·6H2O and glycerol.The AlCl3·6H2O aqueous solution was used to dissolve chitosan (CS) and the CS/poly(vinyl alcohol) (PVA) blend films were prepared at the absence of acetic acid. AlCl3·6H2O was retained in CS/PVA film and glycerol was added to form the complex plasticizer with AlCl3·6H2O. The effect of glycerol on the water sorption, crystalline, thermal and mechanical properties of AlCl3·6H2O doped CS/PVA film was studied by atomic force microscopy, X-ray diffraction, thermal gravity analysis and tensile testing, respectively. The experimental results showed that glycerol had a significant positive effect on the properties of AlCl3·6H2O doped CS/PVA films. With the synergism effect of AlCl3·6H2O and glycerol, the prepared CS/PVA films showed excellent mechanical properties. With the addition of 30 wt% glycerol, the AlCl3·6H2O doped CS/PVA films behave the tensile strength of 39 MPa and elongation at break of 120%, respectively.

Core–shell structured molybdenum disulfide (MoS2) coated polystyrene (PS) microspheres are synthesized with the help of hexadecyl trimethyl ammonium bromide (CTAB) through negative–positive electrostatic attraction. The morphology of the composite particles is studied by scanning electron microscopy (SEM), which apparently provides evidence of MoS2-coated PS. The microspheres’ structure and chemical components are investigated by X-ray diffraction (XRD) and Fourier-transform infrared spectroscopy, respectively. The MoS2/PS composite particles show better thermal stability than PS according to thermogravimetric analysis (TGA). Novel electrorheological (ER) fluids based on the MoS2/PS composite dispersed in silicone oil are prepared and further examined by a rotational rheometer in a controlled shear rate mode under various electric field strengths. The influence of factors such as the electric field strength, the particle sizes, the proportions of the MoS2/PS composite and the functional groups on the surface of PS on ER properties is investigated. The related mechanism of these effects on ER behaviors is also analyzed in detail, aiming to find whether the graphene analogue MoS2 is superior to graphene when making them into ER fluids. MoS2 has reversible and tunable electrorheological characteristics and can transform its phase from a liquid-like to a solid-like state when exposed to an external electric field.

Polyurethanes (PUs) are well-known for their biocompatibility but their intrinsic inert property hampers cell-matrix interactions. Surface modifications are thus necessary to widen their use for biomedical applications. In this work, surface modifications of PU were achieved first by incorporating polyhedral oligomeric silsesquioxane (POSS), followed by alteration of the surface topography via the breath figures method. Subsequently, surface chemistry was also modified by immobilization of gelatin molecules through grafting, for the enhancement of the surface cytocompatibility. Scanning electron microscopy (SEM) was used to verify the formation of highly ordered microstructures while static contact angle, FTIR and XPS confirmed the successful grafting of gelatin molecules onto the surfaces. In vitro culture of human umbilical vein endothelial cells (HUVECs) revealed that endothelial cell adhesion and proliferation were significantly enhanced on the gelatin-modified surfaces, as shown by live/dead staining and WST-1 proliferation assay. The results indicated that the combination of the strategies yielded an interface that improves cell attachment and subsequent growth. This enhancement is important for the development of higher quality biomedical implants such as vascular grafts.

•Three indenoindole-based new organic dyes have been synthesized for DSSCs.•These dyes were designed into a push–pull structure with an ethynylene linker.•All these dyes exhibited high photovoltages and good DSSC performances.•A highest PCE of 8.37% was got by co-sensitization of the dyes QX20 and QX21.Three metal-free push–pull type organic dyes QX19–21 based on indeno[1,2-b]indole donor have been synthesized for dye-sensitized solar cells (DSSCs). In order to obtain good cell performance, an ethynylene linker was inserted into the dye skeleton to extend π-conjugated planar rigid structure and three hexyl groups were involved to prevent dye aggregation. The dyes QX19 and QX20 employing phenylene and thiophene as the π-bridges were designed as a D–π–A structure. As for the dye QX21, a benzothiadiazole was inserted as the secondary acceptor to construct as a D–A–π–A structure. All three dyes based cells exhibited high photovoltages and good DSSC performances. A high PCE of 7.99% was obtained by the dye QX21 under AM 1.5G irradiation. Especially, the co-sensitization of QX21 with QX20 achieved the further improved PCE up to 8.37%.

•The high plasticizing efficiency of LiCl, MgCl2·6H2O, CaCl2, and AlCl3·6H2O on starch/PVA was found.•The plasticizing effects arise from both the interaction between the salts and polymer chains and the high hydrophilicity of these salts.•MgCl2·6H2O and CaCl2 was the more suitable inorganic plasticizers for starch/PVA films than LiCl and AlCl3·6H2O.The effects of different inorganic salts LiCl, MgCl2·6H2O, CaCl2, and AlCl3·6H2O on the crystalline, thermal, water vapor barrier, and tensile properties of starch/PVA films were studied. The high plasticizing efficiency of all these four inorganic salts for starch/PVA film was confirmed by the obtained results. These four salts all had a good compatibility with starch/PVA within the content of 15 wt% and starch/PVA became completely miscible with the addition of 15 wt% inorganic salts. All these four salts had a strong destroying effect on the crystals of starch and PVA. Among these four salts, AlCl3·6H2O had the largest negative effect on the thermal stability of starch/PVA and LiCl had the largest improving effect on the water sorption rate of starch/PVA film. On the whole MgCl2·6H2O and CaCl2 were the more suitable plasticizer for starch/PVA film among these four inorganic salts. With the addition of 15 wt% MgCl2·6H2O and CaCl2, the elongation at break of starch/PVA film could reach to 418.83% and 434.80%, respectively.

•PVA hydrogels were prepared by firstly repeated freezing/thawing process and subsequently soaking in NaCl aqueous solution.•The chain-entanglement network was formed during immersing in NaCl aqueous solution.•The tensile strength and elongation at break of PVA hydrogel could reach up to 1.61 MPa and 631%.High tough poly(vinyl alcohol) (PVA) hydrogels were prepared by repeated freezing/thawing processes and subsequently soaking in saturated NaCl aqueous solution. The PVA hydrogels were characterized via tensile testing, differential scanning calorimetry and scanning electron microscopy respectively. The results showed that during soaking in NaCl aqueous solution the PVA chain-entanglement network was formed and the water was included into the PVA chain-entanglement network. The tensile strength and elongation at break of PVA hydrogel firstly increased with the prolongation of immersing time and then decreased with the immersing time beyond 30 min. By this way the tensile strength and elongation at break of PVA hydrogel could reach up to 1.61 (±0.24) MPa and 631 (±80)%, respectively. This tough PVA hydrogel was prepared at the absence of chemical crosslinker and thus might be considered as a favourable candidate for tissue engineering applications.

•Four novel T-shaped (D)2–A–π–A type organic dyes have been synthesized.•Two triphenylamine donors and an indoloquinoxaline acceptor were combined.•Different acceptors and π-bridges were used to tune the photoelectric properties.•A highest PCE of 7.09% was achieved by the dye QX23.Four novel T-shaped metal-free organic sensitizers QX22–25 based on triphenylamine and indoloquinoxaline have been successfully designed and synthesized as a (D)2–A–π–A type structure. These dye sensitizers have two triphenylamine donors attaching on an indoloquinoxaline-based subordinate acceptor. Different π-bridges (thiophene and furan) and acceptor/anchoring groups (cyanoacrylic acid and 2-(1,1-dicyanomethylene)rhodanine) were involved to tune the photoelectrical properties. Their optical, electrochemical, and photovoltaic properties as well as the DFT calculations have been systematically investigated, indicating these four dyes are all capable as photosensitizers. A highest power conversion efficiency up to 7.09% with a Jsc of 12.9 mA cm−2 and a Voc of 817 mV has been achieved by the dye QX23 with a furan π-bridge and a cyanoacrylic acid acceptor/anchoring group, indicating it is a promising strategy to construct efficient (D)2–A–π–A type sensitizers by incorporating indoloquinoxaline and triphenylamine.

This study was mainly aimed at designing molecular p–n heterojunctions on the surface of N-doped TiO2 for visible-light hydrogen evolution. A series of NiO/N-TiO2 samples were prepared via NH3-postnitridation of nickel oxide-modified TiO2. H2 production from ethanol/water solution was utilized as a model reaction to evaluate the photocatalytic properties of the catalysts. Compared to N-TiO2, a 90-fold-enhanced H2 evolution rate was achieved over the optimal NiO/N-TiO2 catalyst with a 0.5 wt% Ni content. Detailed characterizations clearly showed that loading NiO via wet impregnation leads to high dispersion of Ni2+ species on the surface oxygen vacancy (Vo) sites of the anatase TiO2 nanoparticles, predominantly presenting mononuclear Ti–O–Ni heteroatomic clusters on the surface of TiO2 in the case of low Ni content. These surface heteroatomic clusters can speed up the transfer and separation of photogenerated carriers of N-TiO2. It can thus be established that the molecular Ti–O–Ni heterojunctions are the main contributors to the synergistic enhancement of H2 evolution, whereas NiO nanoclusters are not responsible for the photoactivity. Only one of the N species, N–Ti–Vo, was active and effective for this cooperation with the hydrogen-releasing Ni sites, which can induce ca. 20-fold improvement of hydrogen production over NiO/TiO2 under visible light irradiation.

Tubular-structured nanomaterials with tailorable crystal structures and shell architectures whose properties can be tuned without changing their chemical compositions are attractive in electrochemical energy conversion and storage fields. Herein, we report the fabrication of tubular-structured orthorhombic CoSe2 (o-CoSe2) and cubic CoSe2 (c-CoSe2) by calcining monoclinic Co3Se4 nanotubes (Co3Se4 NTs) prepared by a facile precursor transformation method. Benefiting from advantageous structural features, including functional shells and well-defined interior voids, the tubular-structured o-CoSe2 showed a high power conversion efficiency of 9.34% as a counter electrode catalyst for dye-sensitized solar cells (DSSCs), superior to that of a Pt counter electrode (8.15%), under AM 1.5 G irradiation. In addition, the o-CoSe2 nanotubes also demonstrated excellent electrocatalytic activity in terms of low onset overpotential (∼54 mV) and small Tafel slope (∼65.9 mV per decade) as a hydrogen evolution reaction (HER) catalyst in alkaline medium. Hence, this work provides a promising strategy to selectively design and synthesize highly active electrocatalysts for energy conversion.