Unravelling the Photoelectrochemical Water Splitting of Nanometer-Thick Carbon Nitride Layer.

Matching the thickness of the graphitic carbon nitride (CN) nanolayer with the charge diffusion length is expected to compensate for the poor intrinsic conductivity and charge recombination in CN for photoelectrochemical cells (PEC). Herein, the compact CN nanolayer with tunable thickness is in situ coated on carbon fibers. The compact packing along with good contact with the substrate improves the electron transport and alleviates the charge recombination. The PEC investigation shows CN nanolayer of 93 nm-thick yields an optimum photocurrent of 116 µA cm-2 at 1.23 V versus RHE, comparable to most micrometer-thick CN layers, with a low onset potential of 0.2 V in 1 m KOH under 1 sun illumination. This optimum performance suggests the electron diffusion length matches with the thickness of the CN nanolayer. Further deposition of NiFe-layered double hydroxide enhanced the surface water oxidation kinetics, delivering an improved photocurrent of 210 µA cm-2 with IPCE of 12.8% at 400 nm. The CN nanolayer also shows extended potential in PEC organic synthesis. This work experimentally reveals the PEC behavior of the nanometer-thick CN layer, providing new insights into CN in the application of energy and environment-related fields.

Ultrafine Ni-MoOx Nanoparticles Anchored on Nitrogen-Doped Carbon Nanosheets: A Highly Efficient Noble-Metal-Free Catalyst for Ammonia Borane Hydrolysis.

The development of low-cost and high-efficiency catalysts for the hydrolytic dehydrogenation of ammonia borane (AB, NH3BH3) is still a challenging technology. Herein, ultrafine MoOx-doped Ni nanoparticles (~3.0 nm) were anchored on g-C3N4@glucose-derived nitrogen-doped carbon nanosheets via a phosphate-mediated method. The strong adsorption of phosphate-mediated nitrogen-doped carbon nanosheets (PNCS) for metal ions is a key factor for the preparation of ultrasmall Ni nanoparticles (NPs). Notably, the alkaline environment formed by the reduction of metal ions removes the phosphate from the PNCS surface to generate P-free (P)NCS so that the phosphate does not participate in the subsequent catalytic reaction. The synthesized Ni-MoOx/(P)NCS catalysts exhibited outstanding catalytic properties for the hydrolysis of AB, with a high turnover frequency (TOF) value of up to 85.7 min-1, comparable to the most efficient noble-metal-free catalysts and commercial Pt/C catalyst ever reported for catalytic hydrogen production from AB hydrolysis. The superior performance of Ni-MoOx/(P)NCS can be ascribed to its well-dispersed ultrafine metal NPs, abundant surface basic sites, and electron-rich nickel species induced by strong electronic interactions between Ni-MoOx and (P)NCS. The strategy of combining multiple modification measures adopted in this study provides new insights into the development of economical and high-efficiency noble-metal-free catalysts for energy catalysis applications.

Catalytic CO Oxidation on the Cu+-Ov-Ce3+ Interface Constructed by an Electrospinning Method for Enhanced CO Adsorption at Low Temperature.

It is crucial to eliminate CO emissions using non-noble catalysts. Cu-based catalysts have been widely applied in CO oxidation, but their activity and stability at low temperatures are still challenging. This study reports the preparation and application of an efficient copper-doped ceria electrospun fiber catalyst prepared by a facile electrospinning method. The obtained 10Cu-Ce fiber catalyst achieved complete CO oxidation at a temperature as low as 90 °C. However, a reference 10Cu/Ce catalyst prepared by the impregnation method needed 110 °C to achieve complete CO oxidation under identical reaction conditions. Asymmetric oxygen vacancies (ASOV) at the interface between copper and cerium were constructed, to effectively absorb gas molecules involved in the reaction, leading to the enhanced oxidation of CO. The exceptional ability of the 10Cu-Ce catalyst to adsorb CO is attributed to its unique structure and surface interaction phase Cu+-Ov-Ce3+, as demonstrated by a series of characterizations and DFT calculations. This novel approach of using electrospinning offers a promising technique for developing low-temperature and non-noble metal-based catalysts.

A Full-Spectrum ZnS Photocatalyst with Gradient Distribution of Atomic Copper Dopants and Concomitant Sulfur Vacancies for Highly Efficient Hydrogen Evolution.

A rarely discussed phenomenon in the realm of photocatalytic materials involves the presence of gradient distributed dopants and defects from the interior to the surface. This intriguing characteristic has been successfully achieved in the case of ZnS through the incorporation of atomic monovalent copper ions (Cu+) and concurrent sulfur vacancies (Vs), resulting in a photocatalyst denoted as G-CZS1-x. Through the cooperative action of these atomic Cu dopants and Vs, G-CZS1-x significantly extends its photoabsorption range to encompass the full spectrum (200-2100 nm), which improves the solar utilization ability. This alteration enhances the efficiency of charge separation and optimizes Δ(H*) (free energy of hydrogen adsorption) to approach 0 eV for the hydrogen evolution reaction (HER). It is noteworthy that both surface-exposed atomic Cu and Vs act as active sites for photocatalysis. G-CZS1-x exhibits a significant H2 evolution rate of 1.01 mmol h-1 in the absence of a cocatalyst. This performance exceeds the majority of previously reported photocatalysts, exhibiting approximately 25-fold as ZnS, and 5-fold as H-CZS1-x with homogeneous distribution of equal content Cu dopants and Vs. In contrast to G-CZS1-x, the H adsorption on Cu sites for H-CZS1-x (ΔG(H*) = -1.22 eV) is excessively strong to inhibit the H2 release, and the charge separation efficiency for H-CZS1-x is relatively sluggish, revealing the positive role of a gradient distribution model of dopants and defects on activity enhancement. This work highlights the synergy of atomic dopants and defects in advancing photoactivity, as well as the significant benefit of the controllable distribution model of dopants and defects for photocatalysis.

Hydrophobic Carbon Nitride Nanolayer Enables High-Flux Oil/Water Separation with Photocatalytic Antifouling Ability.

Efficient oil/water separation tackles various issues in occasions of oil leakage and oil discharge, such as environmental pollution, recollection of the oil, and saving the water. Herein, a compact superhydrophobic/superoleophilic graphitic carbon nitride nanolayer coated on carbon fiber networks (CNBA/CF) is designed and synthesized for efficient gravity-driven oil/water separation. The CNBA/CF shows excellent oil absorption and an impressive oil/water filtration separation performance. The flux reaches the state-of-art value of 4.29 × 105 L/m2/h for dichloromethane with separation efficiency up to 99%. Successive oil absorption tests, long-term filtration separation, and harsh conditions experiments confirm the remarkable separation and chemical structure stability of the CNBA/CF filter. Besides, the CNBA/CF demonstrates good photocatalytic antifouling ability thanks to the extended visible light absorption and improved charge separation. This work combines the material surface wettability modulation with a photocatalytic self-cleaning property in the fabrication of efficient oil/water separation materials while overcoming the filter fouling issue.

Efficient and complete dehydrogenation of hydrazine borane over a CoPt catalyst.

Bimetallic CoPt alloy nanoparticles (NPs) immobilized on CeO2 nanorods (CoPt/CeO2) were synthesized by a facile wet-chemistry reduction method, which showed the highest catalytic efficiency reported to date for the complete dehydrogenation of hydrazine borane with a high TOF value of up to 5454 h-1 at 323 K.

Replacing Oxygen Evolution with Hydrazine Borane Oxidation for Energy-Saving Electrochemical Hydrogen Production.

Electrochemical water splitting is a green strategy for hydrogen (H2) production but is severely hindered by the sluggish anodic oxygen evolution reaction (OER). Therefore, replacing the sluggish anodic OER with more favorable oxidation reactions is an energy-saving approach for hydrogen production. Hydrazine borane (HB, N2H4BH3) is considered a potential hydrogen storage material due to its easy preparation, nontoxicity, and high chemical stability. Furthermore, the complete electrooxidation of HB has a unique characteristic of a much lower potential compared to that of OER. All these make it an ideal alternative for energy-saving electrochemical hydrogen production, however, which has never been reported so far. Herein, HB oxidation (HBOR)-assisted overall water splitting (OWS) is proposed for the first time for energy-saving electrochemical hydrogen production. The as-synthesized NiCoP@CoFeP nanoneedle array catalyst exhibited superefficient OER, hydrogen evolution reaction (HER), and HBOR performance. Impressively, NiCoP@CoFeP serves as both anodic and cathodic electrocatalysts for HB-assisted OWS, only requires a low cell voltage of only 0.078 V to achieve a current density of 10 mA cm-2, which was 1.4 V lower than that for HB-free OWS, indicating the highly energy-saving H2 production.

Engineering Electronic and Morphological Structure of Metal-Organic-Framework-Derived Iron-Doped Ni2P/NC Hollow Polyhedrons for Enhanced Oxygen Evolution.

The rational design of an oxygen electrocatalyst with low cost and high activity is greatly desired for realization of the practical water-splitting industry. Herein, we put forward a rational method to construct nonprecious-metal catalysts with high activity by designing the microstructure and modulating the electronic state. Iron (Fe)-doped Ni2P hollow polyhedrons decorated with nitrogen-doped carbon (Fe-Ni2P/NC HPs) are prepared by a sequential metal-organic-framework-templated strategy. Benefiting from the strong electronic coupling, rapid charge-transfer capability, and abundant catalytic active sites, the obtained Fe-Ni2P/NC HPs exhibit an impressive electrocatalytic performance toward the oxygen evolution reaction (OER) with an ultralow overpotential of 228 mV at a current density of 10 mA cm-2 and a small Tafel slope of 33.4 mV dec-1, superior to the commercial RuO2 and most reported electrocatalysts. Notably, this catalyst also shows long durability with an almost negligible activity decay over 210 h for the OER. Combining density functional theory calculations with experiments demonstrates that the doped Fe and the incorporated carbon effectively modulate the electronic structure, enhance the conductivity, and greatly reduce the energy barrier of the rate-determining step in the process of OER. Thus, fast OER kinetics is realized. Moreover, this synthetic strategy can be extended to the synthesis of Fe-NiS2/NC HPs and Fe-NiSe2/NC HPs with excellent OER performance and long-term durability. This work furnishes an instructive idea in pursuit of nonprecious-metal materials with robust electrocatalytic activity and long durability.

Carbon bowl-confined subnanometric palladium-gold clusters for formic acid dehydrogenation and hexavalent chromium reduction.

Formic acid (FA), a high-value product of CO2 hydrogenation and biomass conversion, is considered a promising liquid organic hydrogen carrier for its high hydrogen content, easy accessibility, and relative stability. The development of an efficient heterogeneous catalyst toward FA dehydrogenation and Cr(VI) reduction by FA is needed to boost its sluggish kinetics but still remains a challenge. Herein, uniformly dispersed subnanometric PdAu alloy clusters (i.e., 0.9 nm) were successfully prepared and confined by amine-functionalized carbon bowls (ACB). By virtue of the tiny size and abundant active sites of PdAu clusters, the promotional effect of surface amine groups, and electronic interaction between subnanometric PdAu clusters and support, this as-prepared PdAu/ACB catalyst exhibits superior catalytic property for additive-free FA dehydrogenation (turnover frequency, 10597 h-1 at 323 K) and Cr(VI) reduction (rate constant, 0.47 min-1 at 298 K) under mild conditions, higher than most of the catalysts reported so far. This study offers insight into the design of efficient and durable catalysts for various catalytic applications in energy and environment.

Chromic hydroxide-decorated palladium nanoparticles confined by amine-functionalized mesoporous silica for rapid dehydrogenation of formic acid.

Formic acid (FA), one of the products of biomass conversion and CO2 reduction, has attracted much attention as a renewable liquid hydrogen carrier with a high hydrogen content (4.4 wt%). Searching for efficient catalysts to realize hydrogen evolution from FA are highly desired but challenging. Herein, ultrafine and mono-dispersed Pd-Cr(OH)3 nanoparticles (1.3 nm) loaded on amine-functionalized mesoporous silica (AFMS) have been prepared and applied as an effective catalyst for rapid hydrogen production from additive-free FA. The as-synthesized Pd-Cr(OH)3/AFMS catalysts exhibited efficient catalytic activity and 100% hydrogen selectivity and conversion toward FA dehydrogenation reaction without additives, giving an initial TOF value of 3112 h-1 at 323 K, which is comparable to most of the highly efficient heterogeneous catalysts reported so far under similar reaction conditions. This work provides a feasible idea for the design metal hydroxide-modified Pd-based efficient heterogeneous catalyst, which is expected to enhance the application of FA in fuel cells.

Amine-Functionalized Carbon Bowl-Supported Pd-La(OH)3 for Formic Acid Dehydrogenation.

Formic acid (HCOOH, FA) is emerging as an appealing carrier for hydrogen storage owing to its renewability, a high volumetric capacity of 53 g H2/L, and convenient storage/transportation as a liquid. It is highly desired but still a challenge to search highly efficient catalysts to realize hydrogen evolution from FA. Here, monodispersed and ultrasmall Pd-La(OH)3 nanoparticles (NPs) anchored on amine-functionalized N-doped porous carbon bowl (N-PCB-NH2) substrates have been fabricated through a facile wet chemistry approach. As a result of the ultrafine size of Pd-La(OH)3 NPs (1.6 nm), the deprotonation ability of La(OH)3 and amine groups, and the strong metal-support interaction between Pd-La(OH)3 and N-PCB-NH2, the as-prepared Pd-La(OH)3/N-PCB-NH2 catalyst exhibits 100% H2 selectivity and exceptional catalytic property with a high turnover frequency value up to 9585 h-1 for FA dehydrogenation at 323 K, which is superior to most of the heterogeneous catalysts ever reported. Kinetic isotope effect measurements demonstrate that the C-H bond cleavage is a rate-determining step in the FA dehydrogenation reaction as compared to the O-H bond dissociation. This work presents a feasible approach to synthesize supported ultrafine metal NP catalysts with porous bowl structures for H2 generation from FA.

Adsorption of Transition-Metal Clusters on Graphene and N-Doped Graphene: A DFT Study.

Using the dispersion-corrected density functional theory (DFT-D3) method, we systematically studied the adsorption of 15 kinds of transition-metal (TM) clusters on pristine graphene (Gr) and N-doped graphene (N-Gr). It has been found that TMn (n = 1-4) clusters adsorbed on the N-Gr surface are much stronger than those on the pristine Gr surface, while 3d series clusters present similar geometries on Gr and N-Gr surfaces. The most preferred sites of TMs migrate from hollow to bridge to the top site on the Gr surface along the d series in the periodic table, while the preferred sites of TMs migrate in a much more complex manner on the N-Gr surface. It has also been found that charge transfer decreases along the d series for adsorbed clusters on both surfaces, but adsorbed clusters present less charge transfer on the N-Gr surface than on the Gr surface. What is more interesting is that some TM (Tc, Ru, and Re) clusters change the growth mechanism from the three-dimensional (3D) growth mode on the Gr surface to the two-dimensional (2D) growth mode on the N-Gr surface. At last, it has been found that adsorbed clusters are more dispersed on the N-Gr surface than on the pristine Gr surface due to growth and average aggregation energies.

Porous N-doped carbon with confined Fe-doped CoP grown on CNTs for superefficient oxygen evolution electrocatalysis.

Herein, Fe-doped CoP nanoparticles (Fe-CoP NPs) encapsulated in porous N-doped carbon (PNC)/carbon nanotubes (CNTs) have been successfully synthesized. The Fe doping and confined structures resulted in enhanced charge transfer and improved active sites for intermediates adsorption. The obtained Fe-CoP@PNC/CNTs materials exhibited superefficient OER performance.

Active Site Engineering in CoP@NC/Graphene Heterostructures Enabling Enhanced Hydrogen Evolution.

As the core of an electrocatalyst, the active site is critical to determine its catalytic performance in the hydrogen evolution reaction (HER). In this work, porous N-doped carbon-encapsulated CoP nanoparticles on both sides of graphene (CoP@NC/GR) are derived from a bimetallic metal-organic framework (MOF)@graphene oxide composite. Through active site engineering by tailoring the environment around CoP and engineering the structure, the HER activity of CoP@NC/GR heterostructures is significantly enhanced. Both X-ray photoelectron spectroscopy (XPS) results and density functional theory (DFT) calculations manifest that the electronic structure of CoP can be modulated by the carbon matrix of NC/GR, resulting in electron redistribution and a reduction in the adsorption energy of hydrogen (ΔGH*) from -0.53 to 0.04 eV. By engineering the sandwich-like structure, active sites in CoP@NC/GR are further increased by optimizing the Zn/Co ratio in the bimetallic MOF. Benefiting from this active site engineering, the CoP@NC/GR electrocatalyst exhibits small overpotentials of 105 mV in 0.5 M H2SO4 (or 125 mV in 1 M KOH) to 10 mA cm-2, accelerated HER kinetics with a low Tafel slope of 47.5 mV dec-1, and remarkable structural and HER stability.

Rapid Synthesis of Large-Size Fe2O3 Nanoparticle Decorated NiO Nanosheets via Electrochemical Exfoliation for Enhanced Oxygen Evolution Electrocatalysis.

A novel nonprecious Fe2O3 nanoparticle decorated NiO nanosheet (Fe2O3 NPs@NiO NSs) composite has been obtained by a rapid one-pot electrochemical exfoliation method and can be used as an efficient oxygen evolution reaction (OER) catalyst. In the nanocomposite, the Fe2O3 NPs are uniformly anchored on the ultrathin graphene-like NiO nanosheets. At the same time, we also studied the influence of the Fe/Ni molar ratio on the morphology and catalytic activity. The Fe2O3 NPs@NiO NSs nanocomposite possessed a high BET surface area (194.1 m2 g-1), which is very conducive to the charge/mass transfer of electrolyte ions and O2. Owing to the unique two-dimensional (2D) heterostructures and rational Fe content, the as-prepared Fe2O3 NPs@NiO NSs show high catalytic performance, a low overpotential at 10 mA cm-2 (221 mV), a small Tafel slope (53.4 mV dec-1), and 2000 cycle and 20 h long-term durability. The introduction of Fe2O3 NPs is beneficial to accelerating charge transport, increasing the electrochemically active surface area (ECSA), and thus improving the release of oxygen bubbles from the electrode surface.

Nickel-Ceria Nanowires Embedded in Microporous Silica: Controllable Synthesis, Formation Mechanism, and Catalytic Applications.

Designing highly efficient catalysts for use in fuel production is a highly attractive research area but still remains challenging. Herein, for the first time, ultrafine Ni nanoparticles (NPs) self-assembled on ceria nanowires (NWs) and then embedded in a microporous silica shell (denoted as Ni-CeO2@SiO2) are successfully designed and synthesized via a one-pot facile strategy. The average diameter of Ni-CeO2 NWs is just 2.9 nm, and the length is up to 102.7 nm. The resulting Ni-CeO2@SiO2 exhibits high performance and 100% hydrogen selectivity for H2 production from N2H4 and N2H4BH3 in aqueous solution. Unexpectedly, Ni-CeO2@SiO2 also has good catalytic performance and thermal stability for CO2 methanation. The high catalytic performance of Ni-CeO2@SiO2 can be attributed to the synergistic electronic effect and strong interaction between Ni NPs and CeO2 NWs with plenty of oxygen vacancies, as well as the unique structure effect. As an effective strategy, the present work provides an opportunity to embed ultrafine metal NPs-CeO2 NWs into a microporous silica shell, which has broad application prospects in various catalytic fields.

Anchoring IrPdAu Nanoparticles on NH2-SBA-15 for Fast Hydrogen Production from Formic Acid at Room Temperature.

Hydrogen (H2), a regenerable and promising energy carrier, acts as an essential role in the construction of a sustainable energy system. Formic acid (HCOOH, FA), a natural biological metabolic products and also accessible through carbon dioxide (CO2) reduction, has a great potential to serve as a prospective H2 supplier for the fuel cell. Herein, ultrafine and electron-rich IrPdAu alloy nanoparticles with a size of 1.4 nm are highly dispersed on amine-modified mesoporous SiO2 (NH2-SBA-15) and used as a highly active and selective catalyst for fast H2 production from FA. The as-synthesized IrPdAu/NH2-SBA-15 possesses superior catalytic activity and 100% H2 selectivity with initial turnover frequency values of 6316 h-1 with the additive of sodium formate (SF) and 4737 h-1 even without SF at 298 K, comparable to the most effective heterogeneous catalysts ever published. The excellent performance of IrPdAu/NH2-SBA-15 was not only ascribed to the combination of the electronic synergistic effect of trimetallic alloys and the strong metal-support interaction effect but also attributed to the amine (-NH2) alkaline groups grafted on SBA-15, which is beneficial to boost the split of the O-H bond of FA.

Controlled Synthesis of MOF-Encapsulated NiPt Nanoparticles toward Efficient and Complete Hydrogen Evolution from Hydrazine Borane and Hydrazine.

The catalytic dehydrogenation of hydrazine borane (N2H4BH3) and hydrous hydrazine (N2H4·H2O) for H2 evolution is considered as two of the pivotal reactions for the implementation of the hydrogen-based economy. A reduction rate controlled strategy is successfully applied for the encapsulating of uniform tiny NiPt alloy nanoclusters within the opening porous channels of MOFs in this work. The resultant Ni0.9Pt0.1/MOF core-shell composite with a low Pt content exerted exceedingly high activity and durability for complete H2 evolution (100% hydrogen selectivity) from alkaline N2H4BH3 and N2H4·H2O solution. The features of small NiPt alloy NPs, strong synergistic effect between NiPt alloy NPs and the MOF, and open pore structure for freely mass transfer made NiPt/MIL-101 an excellent catalyst for highly efficient H2 evolution from N2H4BH3 or N2H4·H2O.

Facile Synthesis of Platinum-Cerium(IV) Oxide Hybrids Arched on Reduced Graphene Oxide Catalyst in Reverse Micelles with High Activity and Durability for Hydrolysis of Ammonia Borane.

Highly dispersed Pt-CeO2 hybrids arched on reduced graphene oxide (Pt-CeO2 /rGO) were facilely synthesized by a combination of the reverse micelle technique and a redox reaction without any additional reductant or surfactant. Under a N2 atmosphere, the redox reaction between Ce3+ and Pt2+ occurs automatically in alkaline solution, which results in the formation of Pt-CeO2 /rGO nanocomposites (NCs). The as-synthesized Pt-CeO2 /rGO NCs exhibit superior catalytic performance relative to that shown by the free Pt nanoparticles, Pt/rGO, Pt-CeO2 hybrid, and the physical mixture of Pt-CeO2 and rGO; furthermore, the nanocomposites show significantly better activity than the commercial Pt/C catalyst toward the hydrolysis of ammonia borane (NH3 BH3 ) at room temperature. Moreover, the Pt-CeO2 /rGO NCs have remarkable stability, and 92 % of their initial catalytic activity is preserved even after 10 runs. The excellent activity of the Pt-CeO2 /rGO NCs can be attributed not only to the synergistic structure but also to the electronic effects of the Pt-CeO2 /rGO NCs among Pt, CeO2 , and rGO.

Ruthenium nanoparticles confined in SBA-15 as highly efficient catalyst for hydrolytic dehydrogenation of ammonia borane and hydrazine borane.

Ultrafine ruthenium nanoparticles (NPs) within the mesopores of the SBA-15 have been successfully prepared by using a "double solvents" method, in which n-hexane is used as a hydrophobic solvent and RuCl3 aqueous solution is used as a hydrophilic solvent. After the impregnation and reduction processes, the samples were characterized by XRD, TEM, EDX, XPS, N2 adsorption-desorption, and ICP techniques. The TEM images show that small sized Ru NPs with an average size of 3.0 ± 0.8 nm are uniformly dispersed in the mesopores of SBA-15. The as-synthesized Ru@SBA-15 nanocomposites (NCs) display exceptional catalytic activity for hydrogen generation by the hydrolysis of ammonia borane (NH3BH3, AB) and hydrazine borane (N2H4BH3, HB) at room temperature with the turnover frequency (TOF) value of 316 and 706 mol H2 (mol Ru min)(-1), respectively, relatively high values reported so far for the same reaction. The activation energies (Ea) for the hydrolysis of AB and HB catalyzed by Ru@SBA-15 NCs are measured to be 34.8 ± 2 and 41.3 ± 2 kJ mol(-1), respectively. Moreover, Ru@SBA-15 NCs also show satisfied durable stability for the hydrolytic dehydrogenation of AB and HB, respectively.