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An anode catalyst, FTO-dispersed Co3+-lean and Ovac-free OER-active Co3O4, was developed for the high performance acidic oxygen evolution reaction and proton exchange membrane water electrolysis.

Tetragonal/orthorhombic-bismuth tungstate (t/o-Bi2WO6) homojunctions of high photocatalytic efficiencies were fabricated through a novel in situ Bi induced phase transformation. The photocatalytic efficiencies of t-Bi2WO6 were greatly enhanced via formation of the homojunction. Photocatalytic degradation of rhodamine B (RhB), a recalcitrant organic pollutant, under simulated sunlight illumination was investigated as a demonstration for the efficiency enhancement. A 6.22 folds improvement was achieved with formation of the homojunction in terms of reaction rate constants. The homojunction catalyst was demonstrated to be photocatalytically stable over a five cycles operation. The t/o-Bi2WO6 homojunction enhances separation and utilization efficiency of photo-generated charge carriers and thus greatly boosts the catalytic efficiency. Trapping tests and electron spin resonance spectroscopy were conducted to reveal that singlet oxygen (1O2), hole (h+), electrons (e−), and superoxide anion radical ( O2−) are the main working reactive species for RhB degradation. Density functional theory (DFT) calculations were performed to prove the feasibility of Bi induced phase transformation of t-Bi2WO6 to o-Bi2WO6. The present development offers a new design route for high efficiency photocatalysts for water pollution control.

Enhancing the catalytic efficiency through engineering active site environments is demonstrated for Mo single atom catalysts toward catalyzation of the hydrogen evolution reaction.

Electrochemical energy storage and conversion devices have greatly advanced our daily life in the past few decades because of the convenience and flexibility they provide. As one of the essential components of energy storage and conversion devices, electrode materials play a crucial role in overall device performances. Conventional material preparation methods, including hydrothermal, chemical vapor deposition, high temperature solid phase methods, etc., are often subject to harsh preparation conditions. Therefore, much simpler and more efficient preparation methods are still sought after by the research community. In recent years, ion exchange (IE) technology, as a novel method for syntheses of nanomaterials, has attracted a great deal of research attention for its great capability in precise structural design and simultaneous regulation of component compositions. Nevertheless, the links among reaction mechanisms, resulting products, and product application performances, have not been fully elaborated. Herein, this review systematically summarizes historical developments of the IE technology for preparation of nanomaterials and relevant reaction mechanisms from both kinetic and thermodynamic perspectives. A detailed summary of recent applications of the IE technology for preparation of a wide variety of nanomaterials and their applications in electrochemical energy storage and conversion devices, including supercapacitors, lithium/sodium-ion batteries, electrolytic water splitting, and hydrogen fuel cells, is presented. In-depth understanding of the IE technology provides better technical approaches for fabrication of high-performance electrode materials. In the final section, an outlook on the IE technology is offered.

Background Triclosan, a broad-spectrum bacteriostatic germicide, is widely used in daily life. Traditional methods for removal of triclosan however suffer from possible secondary pollution. Photocatalytic technology is considered one of the most promising methods because of its low cost and high efficiencies, which removes pollutants through direct utilization of solar energy. Methods Here, a heterostructured composite photocatalyst Bi7O9I3/Bi was prepared through an in situ reduction method for photocatalytic degradation of triclosan, with the degradation mechanism investigated with a free radical trapping experiment and an electron spin resonance (ESR) method. Furthermore, the effects of the presence of inorganic ions on the degradation efficiencies were investigated. Findings Compared with Bi7O9I3, the degradation efficiency of Bi7O9I3/Bi on triclosan was significantly improved. This is mainly attributed to the formation of Bi nanoparticles on the surface of Bi7O9I3, which effectively promotes the light absorption through surface plasmon effects of Bi and separation of photo-generated electron-hole pairs through band structure modulation, thereby greatly improving the photocatalytic performances. The photo-generated electrons (e−) and superoxide radicals (·O2−) were found to be the main active species for triclosan degradation. Furthermore, the presence of NO3−, SO42- and Cl− all hamper the photodegradation of triclosan, whereas HCO3−, Ca2+ and Mg2+ inhibit or promote it depending on their concentrations.

The lithium-ion capacitor (LIC) is a novel energy storage device, pairing battery-type anodes with capacitor-type cathodes, capable of delivering high energy and power densities. The anode material...

Lithium–sulphur batteries (LSBs) have been drawing rapidly increasing research attention because of the low cost and high theoretical capacity of sulphur. The applications of LSBs however are hampered by poor stability caused by the shuttle effects of lithium polysulphides (LiPS), poor conductivities of sulphur, and sluggish redox kinetics of LiPS. Here, an advantageous carved N-doped carbon nanobox structure triply functionalized with an FeCoNi trimetallic sulphide was developed as a high performance sulphur host for LSBs. The strong chemical interactions toward LiPS, half-metallic conductivities, and catalytic activities toward redox reactions of LiPS, enabled through functionalization with FeCoNi trimetallic sulphide, work together to resolve the critical issues of LSBs. Moreover, the carved N-doped carbon nanobox structure serves as a nanoreactor that helps retain LiPS at cathodes and offers a confined space for fast local redox reactions. The triply functionalized carved N-doped carbon nanoboxes (S-FeCoNi@C-CNB) lead to high performance LSBs, delivering a high capacity of 1238 mA h g−1 at 0.1C and maintaining a decent capacity of 655 mA h g−1 at 2C. The LSB exhibits excellent stability with a low capacity decay rate of 0.049% per cycle over 200 cycle operations at 1C, indicating the success of S-FeCoNi@C-CNB in suppressing the shuttle effect.

N-doped carbon armored metal phosphides were anchored in-situ on backbones of nickel foam (NF), by using polydopamine as both carbon source and targeted precursor delivery vehicle. The product served as a highly efficient chainmail bi-functional catalyst toward electrolytic water splitting, requiring small operating cell voltages of only 1.65, 1.73, and 1.79 V at 50, 100, and 250 mA/cm2, respectively for overall water splitting. More importantly, the product catalyst also possessed excellent long-term stability, even tested at 250 mA/cm2. The excellent activity and durability may be ascribed to the positive synergistic effects between well-mixed metal phosphides, advantageous nanostructure of interwoven thin vertical nanosheets, protective and conductive N-doped carbon matrix, hydrophilic and aerophobic characteristics, and well dispersed and utilized active materials on skeleton surfaces of the highly conductive NF. This synergistic effect boosting and protective layer armored design for highly efficient and stable electrocatalysts is unique and scalable, suitable for large-scale applications not only in the field of electrocatalysis, but also in other heterogeneous catalysis.

Electrocatalytic hydrogen production driven by surplus electric energies is considered a promising sustainable process for hydrogen supply. The high overpotential and low energy-conversion efficiency caused by the slow kinetics of the four-electron transfer oxygen-evolution reaction (OER), however, hamper its competitiveness. Herein, a highly stable, efficient OER catalyst was developed, taking the effects of both composition and nanostructure into account for the catalyst design. N-doped carbon-armored mixed metal phosphide nanoparticles confined in N-doped porous carbon nanoboxes, a particle-in-box nanostructure, were synthesized from monodisperse Ni3[Fe(CN)6]2·H2O nanocubes through sequential conformal polydopamine coating, ammonia etching, and thermal phosphorization. The product exhibited outstanding catalytic abilities for the OER in 1.0 M KOH, delivering 10, 100, and 250 mA/cm2 at ultrasmall overpotentials of 203, 242, and 254 mV, respectively, with an ultrasmall Tafel slope of 38 mV/dec, outperforming most recently reported top-notch iron-group-based OER catalysts. The long-term stability was also excellent, showing a small chronopotentiometric decay of 2.5% over a 24 h operation at 50 mA/cm2. The enhanced catalytic efficiency and stability may be attributable to the unique particle-in-box structure as a nanoreactor offering a local, fast reaction environment, the conductive N-doped porous carbon shell for fast charge and mass transport, the synergistic effect between multicomponent metal phosphides for enhanced intrinsic activities, and the carbon protection layer to prevent/delay the catalyst core from being deactivated. This combined particle-in-box and chainmail design concept for electrocatalysts is unique and advantageous and may be readily applied to the general field of heterogeneous reactions.

The key to develop efficient catalysts is to improve the quantity and activity of catalytic sites of the catalysts through optimal structural and compositional design. Accordingly, open-mouth N-doped carbon nanoboxes embedded with mixed metal phosphide nanoparticles are fabricated from monodisperse Ni3[Fe(CN)6]2·H2O nanocubes through conformal Ni3[Co(CN)6]2·12H2O layer coating, ammonia etching, and thermal phosphorization, sequentially. The product catalyst exhibits highly efficient electrocatalytic performances, achieving low overpotentials of 204 and 129 mV for the oxygen evolution reaction and hydrogen evolution reaction, respectively, and a small working voltage of 1.57 V for the overall water splitting, all at 10 mA cm-2. Its long-term electrocatalytic stability is also outstanding, experiencing only minor chronopotentiometric decay after a 24 h operation at 10 mA cm-2. The enhanced electrocatalytic performance may be attributed to the synergistic effects between the mixed metal phosphides, the protective function offered by the chainmail catalyst design, and the fast mass transport channels for the electrolyte and gaseous products afforded by the large openings on the nanobox shell, as well as the easy access of the inner active sites of the nanobox. The ingenious open-mouth nanobox structure together with embedded mixed metal phosphide nanoparticles is a unique design for improving the quantity and activity of catalytic sites of the catalyst for high efficiency electrolytic water splitting. The present design concept can be readily applied to the fabrication of other heterogeneous catalysts.

Developments of non-precious metal based active and stable catalysts are of great importance and challenge to green hydrogen production from acidic electrocatalytic water splitting. Design of composite catalysts with synergy between active and stable components proves to be a promising approach. Herein, N-doped carbon armored Co

MIL-101(Cr), a subclass of metal–organic frameworks (MOFs), is a promising adsorbent for carbon dioxide (CO2) removal due to its large pore volume and high surface area. Solvent-free synthesis of MIL-101(Cr) was employed in this work to offer a green alternative to the current approach of synthesizing MIL-101(Cr) using a hazardous solvent. Characterization techniques including XRD, SEM, and FTIR were employed to confirm the formation of pure MIL-101(Cr) synthesized using a solvent-free method. The thermogravimetric analysis revealed that MIL-101(Cr) shows high thermal stability up to 350 °C. Among the materials synthesized, MIL-101(Cr) at the molar ratio of chromium precursor to terephthalic organic acid of 1:1 possesses the highest surface area and greatest pore volume. Its BET surface area and total pore volume are 1110 m2/g and 0.5 cm3/g, respectively. Correspondingly, its CO2 adsorption capacity at room temperature is the highest (18.8 mmol/g), suggesting it is a superior adsorbent for CO2 removal. The textural properties significantly affect the CO2 adsorption capacity, in which large pore volume and high surface area are favorable for the adsorption mechanism.

A self-assembled mesoporous silica sphere templating process was developed to create hierarchical continuous porous coral reef like N-doped carbon nanostructures on stainless steel meshes as bifunctional electrodes for ultrahigh performance lithium ion based energy storage devices. The coral reef like carbon nanostructure achieved a high specific surface area of 1229 m2 g−1 and a large specific pore volume of 2.21 cm3 g−1, without application of chemical activations. The electrode, when serving as an anode for lithium ion batteries (LIB) or lithium ion capacitors (LIC), delivered an ultrahigh specific capacity of 2058 mAh g−1 at 0.2 A g−1. If used as a cathode for LICs, it generated a high specific capacity of 125 mAh g−1 at 0.1 A g−1. The LICs assembled from using the electrode as both the cathode and anode, exhibited a high energy density of 145 Wh kg−1 at a power density of 1.4 kW kg−1 and maintained an energy density of 58 Wh kg−1 under an ultrahigh power density of 27.3 kW kg−1, among the top tie of the state-of-the-art LICs. The cycling stability of the LIC was outstanding with a 85% capacity retention after 5000 cycle operations at 5 A g−1. The hierarchical continuous porous coral reef like N-doped carbonaceous nanostructure provides micropores as micro-reservoirs of Li ions for local and fast Li ion intercalation/de-intercalation, edge N-doping for additional redox pseudo-capacitances, and large pore volumes to accommodate the volume expansion/shrinkage at the charge/discharge cycles and to offer fast mass transfer path for electrolyte ions, altogether leading to the successful applications as bifunctional electrodes for Li ion based energy storage devices.

A N-doped hierarchical porous carbon nanostructure (NHPCN) was created on a carbon cloth (CC), through a templating process using self-assembled mesoporous silica spheres as the template, to fabric...

Ultraviolet (UV) light irradiation on CeO2 nanocrystals catalysts has been observed to largely increase the material’s catalytic activity and reactive surface area. As revealed by x-ray absorption near edge structure (XANES) analysis, the concentration of subvalent Ce3+ ions in the irradiated ceria samples progressively increases with the UV-light exposure time. The increase of Ce3+ concentration as a result of UV irradiation was also confirmed by the UV-vis diffuse reflectance and photoluminescence spectra that indicate substantially increased concentration of oxygen vacancy defects in irradiated samples. First-principle formation-energy calculation for oxygen vacancy defects revealed a valence-hole-dominated mechanism for the irradiation-induced reduction of CeO2 consistent with the experimental results. Based on a Mars-van Krevelen mechanism for ceria catalyzed oxidation processes, as the Ce3+ concentration is increased by UV-light irradiation, an increased number of reactive oxygen atoms will be captured from gas-phase O2 by the surface Ce3+ ions, and therefore leads to the observed catalytic activity enhancement. The unique annealing-free defect engineering method using UV-light irradiation provides an ultraconvenient approach for activity improvement in nanocrystal ceria for a wide variety of catalytic applications.

We developed a unique photocatalyst, CuFe2O4 nanoparticles decorated on partially reduced graphene oxides, to selectively and efficiently cleave lignin model compounds into value-added aromatic chemicals via a sun-light assisted heterogeneous Fenton process. Through proper design of the photocatalyst composition and reaction conditions, controlled oxidative cleavage of the lignin model compound was achieved to produce high-value aromatic chemicals, guaiacol and 2‑methoxy‑4-propylphenol, in high yields, instead of complete mineralization of the lignin model compound. The CuFe2O4 nanoparticles effectively catalyze the generation of highly oxidative free radicals from the oxidant, H2O2, for β-O-4 bond cleavage. The partially reduced graphene oxides serve as the large size support to accommodate and immobilize the CuFe2O4 nanoparticles for easy recycling of the catalyst, to attract the lignin model compounds through π–π stacking and hydrogen bonding for efficient cleaving reaction, and to accelerate transport of photo-induced electrons for better charge separation and thus higher photocatalytic activities. At optimal conditions, yields of 72.6% and 52.5% were achieved for guaiacol and 2‑methoxy‑4-propylpheno, respectively in 60 min at room temperature and under ambient pressures.

TixFe1−xOy shells, in-situ formed from thermal treatment of a Ti-containing metal organic framework, NH2-MIL-125(Ti), significantly boost the photoelectrochemical water oxidation efficiency of Fe2O3 nanorod cores. The NH2-MIL-125(Ti) was coated on the surface of the Fe2O3 nanorods with a solvothermal process, followed by a two step calcination to afford the TixFe1−xOy shell/Fe2O3 core nanorod arrays. The TixFe1−xOy shell/Fe2O3 core nanorod array electrode exhibited much improved photoelectrochemical activities over the pristine Fe2O3 nanorod array electrode, boosting photo-current densities to 26.7 folds of that achieved by the pristine Fe2O3 nanorod array electrode at 1.23 V (vs. RHE) under illumination of simulated sun light of AM 1.5 G. The success may be attributed to the much enhanced charge separation enabled by the hole trapping heterojunction of TixFe1−xOy shell/Fe2O3 core. The photoelectrochemical stability of the TixFe1−xOy shell/Fe2O3 core nanorod array electrode was excellent, retaining 98.9% of the initial photo-current density after a 5 h continuous operation. This work is the first demonstration of MOF derived core-shell heterojunction for large improvements of PEC water splitting efficiencies, and can be readily extended to a wide range of catalyst design.

Metal-organic framework (MOF), possessing versatile catalytic activities, remarkable structural diversity, high surface areas, and tunable pore sizes, was recently demonstrated an outstanding catalyst for electrolytic water splitting. The electrolytic performances can be much enhanced with a synergistic design of the MOFs, which was realized as uniformly well-mixed and dispersed Fe- and Ni-MOFs (termed as MFN-MOFs) in-situ grown on backbones of nickel foam (NF). The electrocatalyst thus developed exhibited ultra-high activities at high current densities for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in 1 M KOH, delivering 10 and 500 mA cm−2 at ultralow overpotentials of 79 and 234 mV, respectively with a small Tafel slope of 30.1 mV dec−1 for the HER and achieving ultralow overpotentials of 235 and 294 mV for the OER at 50 and 500 mA cm−2, respectively with a small Tafel slope of 55.4 mV dec−1. The inter-molecular synergistic interactions between the well-mixed and dispersed Fe- and Ni-MOFs not only facilitate the critical charge transfer for the redox reactions but also disperse the active metal ion sites to enhance their degree of utilization to achieve exceptional OER and HER performances. The MFN-MOFs/NF//MFN-MOFs/NF couple exhibited ultralow cell voltages of 1.495 V@10 mA cm−2 and 1.80 V@500 mA cm−2 with a Tafel slope of only 79.5 mV dec−1 in 1 M KOH, outperforming most of the state-of-the-art bifunctional electrode couples and benchmark couple of Pt-C/NF//IrO2/NF. More importantly, the MFN-MOFs/NF electrode exhibited ultrastability at high current densities, with a minor decay of 3.7% in a chronopotentiometric stability test conducted at a commercially viable high current density of 500 mA cm−2 for overall water-splitting over 100 h. This synergistic effect boosting design concept for electrocatalysts was successfully demonstrated, opening up a new way for catalyst design toward large-scale H2 production.

Development of stable and efficient non-noble metal based electrocatalysts for oxygen evolution reaction (OER) in acidic media is of great importance for proton exchange membrane based water electrolysis, which is indispensable for green hydrogen production. Herein, iron-doped, carbon-coated Co3O4 nanocomposite derived from a cobalt metal-organic framework, is grown in-situ on fluorine-doped tin oxide (FTO) glass (Fe-Co3O4@C/FTO) as an efficient and a stable binder-free electrode for acidic OER. Fe doping enhances both catalytic efficiency and stability of carbon coated Co3O4 toward acidic OER, through inducing small primary particle sizes and suitably modulated electronic structure of Co3O4, and better catalyst/substrate adhesion. Fe-Co3O4@C/FTO exhibits impressive electrocatalytic performances in 0.5 M H2SO4, with a low overpotential of 396 mV at 10 mA cm−2 and a small Tafel slope of 68.6 mV dec−1. Its electrochemical performances remain stable for over 50 h at 10 mA cm−2, making it a promising non-noble metal based electrocatalyst for acidic OER.

Conducting porous substrates of high hydrophilicity are advantageous in applications of electrochemical biosensors as host electrodes, offering not only fast charge transport and large sensing surface areas but also necessary wettability in aqueous analytes. In this study, inexpensive, highly hydrophilic (contact angle < 5°), conducting (sheet resistance of 17 Ω □−1) porous fluorine-doped tin oxide (FTO) glass is fabricated from commercial FTO glass with a novel, simple, one-step Sn4+-based anodic treatment process, and used as a host electrode for electrochemical biosensors. We demonstrate its superior performance with hydrogen peroxide sensing. The hydrogen peroxide sensor is fabricated by simply depositing Pt nanoparticles onto the surface of the porous FTO substrate (PFTO) with a polyol process. Pt-decorated commercial FTO (CFTO) is also investigated as a control. The sensitivity achieved with the Pt-decorated PFTO is almost one order of magnitude higher than that of the Pt-decorated CFTO (25.8 vs. 2.69 mA M−1), and the response time is shortened from 36 s for the Pt-decorated CFTO to 1 s for the Pt-decorated PFTO. The PFTO proves to be a promising electrode substrate for host functional materials in electrochemical biosensors and can be readily applied to sensing of a wide variety of biosubstances.

Syngas, consisting of equimolar CO and H2, is an important feedstock for large-scale production of a wide range of commodity chemicals including aldehyde, methanol, ammonia, and other oxygenated chemicals. Dry reforming of methane (DRM), proceeding by reacting greenhouse gases, CO2 and CH4, at high temperatures in the presence of a metal catalyst, is considered one of the most environmentally friendly routes for syngas production. Nevertheless, nonprecious metal-based catalysts, which can operate at relatively low temperatures for high product yields and selectivities, are required to drive the DRM process for industrial applications effectively. Here, we developed NiCo@C nanocomposites from a corresponding NiCo-based bimetallic metal-organic framework (MOF) to serve as high-performance catalysts for the DRM process, achieving high turnover frequencies (TOF) at low temperatures (>5.7 s-1 at 600 °C) and high product selectivities (H2/CO = 0.9 at 700 °C). The incorporation of Co in Ni catalysts improves the operation stability and light-off stability. The present development for MOF-derived nanocomposites opens a new horizon for design of DRM catalysts.

Lithium sulfur batteries (LSBs) are regarded as one of the most promising energy storage devices because of their ultrahigh theoretical energy densities (2500 Wh kg-1), low cost, and environmental friendliness. Nevertheless, several detrimental drawbacks, including shuttling effects caused by soluble lithium polysulfides (LiPS), sluggish conversion kinetics between LiPS, and poor conductivities of sulfur, prevent commercialization of LSBs. To takle the above issues, MOF-derived cobalt disulfide/nitrogen-doped carbon (NC) composite polyhedrons linked with multi-walled carbon nanotubes (MWCNTs), CoS2@NC/MWCNT, were developed as an effective sulfur host for LSBs. It was fabricated through first in-situ growth of nanoporous ZIF-67 on surface treated MWCNTs, followed by carbonization and sulfurization. CoS2@NC/MWCNT combines the advantages of outstanding conductivities of MWCNTs, excellent chemical adsorption of NC and CoS2 toward LiPS, and high catalytic efficiency of CoS2 toward LiPS conversion, effectively addressing the shuttling, sluggish conversion, and low conductivity issues. The CoS2@NC/MWCNT electrode delivered a high specific capacity of 1133 mAh g-1 at 0.1 C and maintained a decent specific capacity of 607 mAh g-1 at 2.0 C. Its cycling stability is excellent, with a capacity retention rate of 77% after 300 cycles at 1.0 C, i.e., an average capacity decay rate of 0.078% per cycle. The cycling stability was further improved through increasing N-doping levels of the carbons for enhanced chemical adsorption toward LiPS and through incorporation of inter-linked reduced graphene oxide sheets as a physical barrier to reduce the diffusion loss of LiPS, achieving even smaller capacity decay rates of 0.066 and 0.064 % per cycle, respectively.

Controlled synthesis of metal–organic framework (MOF)-derived Mg-Zn hybrid nanostructure was demonstrated for the development of basic catalysts applied in biodiesel production from soybean oil. Two types of Mg-Zn hybrid nanostructures were successfully fabricated under different atmospheres (Ar, air), (1) MgO nanoparticles encapsulated in Zn-based MOF (MgO@Zn-MOF) and (2) MgO nanoparticles uniformly decorated on ZnO nanoparticles derived from Zn-MOF (MgO@ZnO), respectively. Ultrafine MgO nanoparticles (

A simple one-step passivator-modulated nickel foam (NF) anodization process was developed to fabricate synergistically well-mixed NiO/α-Fe2O3@NF, which was demonstrated a high efficiency electrocatalyst for oxygen evolution reaction (OER), exhibiting ultralow overpotentials and excellent stability at high current densities. The NiO/α-Fe2O3@NF composite electrode, with NiO and α-Fe2O3 well-mixed at nanoscale for much enhanced synergistic effects, exhibited extraordinary electrochemical activities with ultralow overpotentials of 244 and 334 mV at current densities of 50 and 500 mA/cm2, respectively, for the OER in 1 M KOH. The NiO/α-Fe2O3@NF composite electrode was further tested as both the cathode and anode for overall water splitting, and achieved low working cell voltages of 1.76 and 1.99 V at the current densities of 50 and 500 mA/cm2, respectively, outperforming the pairing of Pt/C@NF and IrO2@NF, 1.79 and 2.08 V, correspondingly. The stability of the NiO/α-Fe2O3@NF electrode was also outstanding, exp...

A cocktail strategy was developed to fabricate sandwich nanostructure of hydrogenated C-doped anatase TiO2 nanocrystals/N-doped carbon dots@layer/rutile TiO2 nanorod array as an efficient photocatalyst for photoelectrochemical water oxidation. The one-dimensional, single crystalline nature of the innermost rutile TiO2 nanorod facilitates charge transport. The middle N-doped carbon dots@layer offers dual functionalities, with the N-doped carbon dots as the photosensitizer to harvest long wavelength lights and the N-doped carbon layer as the conductive layer for fast charge transport toward the current collector. The outermost hydrogenated C-doped anatase TiO2 nanocrystals serve to increase the visible light absorption and to form a type II heterostructure with the innermost rutile TiO2 nanorods to enahnce the charge separation. An enhancement of 86% in photocurrent density was achieved at 1.23 V (vs. RHE) under illumination of simulated sun light of 100 mW/cm2 by the sandwich nanostrcuture, as compared to that of the plain rutile TiO2 nanorod array. The enhancement was boosted to 228% under visible simulated sun light (λ > 400 nm) illumination. The photoconversion efficiency and photocurrent density retention rate were significantly improved from 0.23% and 60% for the plain rutile TiO2 nanorod array to 0.65% and 84% for the sandwich nanostructure, respectively.

Power conversion efficiencies of perovskite solar cells depend heavily on the uniformity, coverage, grain size, and thickness of the perovskite layer. In this study, hybrid perovskite CH3NH3PbI3-xBrx thin films were fabricated from porous PbI2-xBrx layers prepared with a mixture solvent pore generation treatment process. The mixture solvent is composed of two anti-solvents of PbI2-xBrx to promote its crystallization, one with a low boiling point to accelerate the evaporative removal of the solvents of PbI2-xBrx, dimethylformamide (DMF) and dimethyl sulfoxide (DMSO), and the other with a high boiling point to modulate the evaporative removal of DMF and DMSO to achieve a suitably configured porous structure for the PbI2-xBrx layer. With this fast pore generation treatment, uniform porous PbI2-xBrx layers were obtained within minutes, far more efficient than previously reported pore generation processes. The uniform porous PbI2-xBrx layer enabled formation of hybrid perovskite CH3NH3PbI3-xBrx thin films of low PbI2-xBrx residue, good crystallinity, low defect concentrations, and long charge carrier life times. The champion cell, assembled from the optimal hybrid perovskite thin films fabricated from optimized pore generation treatments, exhibited significantly superior power conversion performances of 19.26 mA/cm2 for the short circuit current density, 1.01 V for the open circuit voltage, 0.68 for the fill factor, and 13.16% for the power conversion efficiency, as compared to the average power conversion efficiency of 10.03% for non-porous PbI2-xBrx layer based cells.

TiO2 nanocrystals decorated core-shell CdS-CdO nanorod arrays, TiO2@CdO/CdS NR, were fabricated as high efficiency anodes for photoelctrochemical hydrogen generation. The novel sandwich heterostructure was constructed from first growth of CdS nanorod arrays on a fluorine doped tin oxide (FTO) substrate with a hydrothermal process, followed by in situ generation of CdO thin films of single digit nanometers from the CdS nanorod surfaces through thermal oxidation, and final decoration of TiO2 nanocrystals of 10–20 nm via a successive ionic layer absorption and reaction process. The core-shell CdS-CdO heterostructure possesses a Z-scheme band structure to enhance interfacial charge transfer, facilitating effective charge separation to suppress electron-hole recombination within CdS for much improved current density generation. The final decoration of TiO2 nanocrystals passivates surface defects and trap states of CdO, further suppressing surface charge recombination for even higher photovoltaic conversion efficiencies. The photoelectrochemical performances of the plain CdS nanorod array were significantly improved with the formation of the sandwich heterostructure, achieving a photo current density of 3.2 mA/cm2 at 1.23 V (vs. RHE), a 141% improvement over the plain CdS nanorod array and a 32% improvement over the CdO/CdS nanorod array.

Novel particle-in-box nanostructure was developed and demonstrated as a high performance bifunctional catalyst for electrochemical overall water splitting. The particle-in-box nanostructure was composed of N-doped graphene layer coated Fe-Ni alloy nanoparticles encapsulated within an N-doped carbon hollow nanobox. The nanobox serves as a nanoreactor with the reactant, water, and catalyst nanoparticles confined within for intimate contact and effective reaction. The particle-in-box nanostructure was created through a spatially confined pyrolysis process by taking polydopamine coated Ni3[Fe(CN)6]2·H2O nanocubes as the precursor, calcination of which leading to formation of an N-doped porous carbon shell from the carbonization of the polydopamine coating layer and formation of interior N-doped graphene layer coated Fe-Ni alloy nanoparticles from reduction of both iron and nickel ions and graphitization of the CN groups. The particle-in-box nanostructured catalyst exhibited excellent electrocatalytic activities, achieving overpotentials of 270 and 201 mV for the oxygen and hydrogen evolution reactions, respectively at 10 mA/cm2, and thus is suitable of serving as a high performance bifunctional catalyst for the overall water splitting reaction, achieving a low full cell overpotential of 471 mV at 10 mA/cm2. The excellent electrocatalytic activity may be attributed to the advantageous particle-in-box nanostructure offering confined and effective reaction environment and the synergistic effects resulting from the conductive, hollow, and porous carbon shell and the small size of the Fe-Ni alloy nanoparticle core and its N-doped graphene layer shell. This new nanostructure of particle-in-box is superior and advantageous for a wide range of applications, not only for electrocatalytical reactions but also for other heterogeneous reaction systems.

Solvent engineering with dimethylsulfoxide (DMSO) has been shown to achieve high quality methylammonium lead iodide (MAPbI3) films for high performance perovskite solar cells (PSC). The morphology and composition of the intermediate PbI2-DMSO films play the key role for the success. The coordination and crystal growth of the PbI2–DMSO film however remain un-exploited. We study the way and extent of DMSO coordination and subsequent crystal growth of the PbI2-DMSO film to fabricate high quality perovskite films for enhancement of the photovoltaic performances of the cells. The DMSO is pre-coordinated or coordinated in-situ with PbI2 at a 1:1 or 2:1 M ratio. The PbI2-DMSO film from pre-coordination at 1:1 M ratio gives perovskite films of the best quality, being dense and possessing uniform size grains, high light absorption, and long charge carrier life times, among all investigated. The champion PSC achieves a high power conversion efficiency of 15.2%, significantly outperforming 13.0% of PSC based on PbI2-DMSO films from in-situ coordination at 1:1 M ratio, and 11.7% of PSC based on plain PbI2 films.

Core/shell p-BiOI/n-β-Bi2O3 heterojunction arrays were successfully fabricated with a simple solvothermal method followed by calcination. The p-n junction electrode was characterized with X-ray diffraction spectroscopy, field emission scanning electron microscope, high resolution transmission electron microscope, X-ray photoelectron spectroscopy, UV–visible diffuse reflectance spectra, and photocurrent responses. The photoelectrochemical water splitting efficiency of the plain BiOI array was significantly improved through in-situ formation of the β-Bi2O3 shell via a simple calcination treatment to form the core/shell p-BiOI/n-β-Bi2O3 heterojunction array. The success in boosting the efficiency was attributed to the much enhanced charge separation facilitated by the internal electric field established by the p-n junction, formation of the type-II band structure, and the excellent interfacial contact between the BiOI and β-Bi2O3 domains enabling smooth charge transport across the interface.

Global warming issue due to the excessive carbon dioxide gas emission have raised strong interest in capturing or reducing the CO2 from flue gas or atmosphere. Physisorption-based CO2 capture applying the metal organic framework (MOF) provides a promising alternative for capturing CO2 due to the simplicity, low operating cost, and low energy requirement of the adsorption approach combined with the high CO2 adsorption capacity MOF material. In this study, a series of Chromium based MIL MOF with a variety molar ratio of chromium metal to 1,4-Benzene Dicarboxylate (BDC) organic linker were prepared via the solvent-free method (mechanochemical) to develop a clean and efficient way of synthesising MOF samples as promising CO2 adsorbents. The XRD results and FTIR spectra have confirmed the successful fabrication of MIL-101(Cr) MOF using the solvent-free method. The SEM images illustrated fine growth of irregular shaped coarse particles for Cr MOF with equal mole ratio of Cr to BDC. The MIL-101(Cr) samples were also tested on their CO2 adsorption capacity to understand the influence of molar ratio of the starting materials on the CO2 adsorption capacity. It was found that the MIL-101(Cr)1 led to the formation of a product with the highest CO2 uptake capacity of 18.78 mmol/g. In contrast, the EDS analysis result revealed that all the samples synthesised in this work were well incorporated with the Chromium element. It is therefore suggested that the molar ratio of Cr to BDC plays a critical role in determining the CO2 gas adsorption capacity.

Bifunctional multi-component electrocatalyst, (NixFeyCo6-x-y)Mo6C, developed based on volcano plots of suitable descriptors, achieves ultralow overpotentials of 20 and 194 mV for hydrogen evolution reaction (HER) and 212 and 336 mV for oxygen evolution reaction (OER) at current densities of 10 and 500 mA cm−2, respectively. When serving as both anode and cathode for overall water splitting, it requires ultralow cell voltages of only 1.47 and 1.77 V to deliver current densities of 10 and 500 mA cm−2, respectively and exhibits ultrastability, experiencing chronoamperometric decay of only 6.2 % at an ultrahigh initial current density of 500 mA cm−2 for 50 h. The outstanding OER performances may be attributed to formation of and synergistic effects between multiple active intermediates during the OER, as revealed with an in-situ Raman spectroscopic study. With an in-situ X-ray absorption spectroscopic examination, the HER is identified to proceed through the Volmer-Heyrovsky route.

Mixed NiO/NiCo2O4 nanocrystals grown in situ from the skeleton of a 3D porous nickel network (3DPNN) were prepared with a simple hydrothermal method followed by a low temperature calcination, exhibiting outstanding electrocatalytic efficiencies toward oxygen evolution reactions (OER). The 3DPNN was prepared with a novel leaven dough method and served as both the nickel source for growth of the mixed NiO/NiCo2O4 nanocrystals and the charge transport highway to accelerate the sluggish kinetics of the OER. The mixed NiO/NiCo2O4 nanocrystals exhibited pronounced synergistic effects to achieve a high mass activity of 200 A g–1 at the catalyst mass loading of 0.5 mg cm–2, largely outperforming the corresponding single component nanocrystal systems, NiO (5.87) and NiCo2O4 (9.35). The NiO/NiCo2O4@3DPNN composite electrocatalyst achieved a low overpotential of 264 mV at the current density of 10 mA cm–2 and 389 mV at the practically high current density of 250 mA cm–2, which compete favorably among the top tier of...

A superfast, room-temperature, one-step carrier-solvent-assisted interfacial reaction process was developed to prepare Ag/AgFeO2 composite nanocrystals (NCs) of less than 10 nm in size within a 1 min reaction time. These composite NCs were with a direct energy band gap of 2.0 eV and were paramagnetic, making them suitable for optical activation and magnetic manipulation. These composite NCs, applied as a photocatalyst for the treatment of HeLa cells, achieved a significant reduction of 74% in cell viability within 30 min. These Ag/AgFeO2 composite NCs proved to be a promising magnetically guidable photocatalyst for cancer cell treatment.