Applications of adsorption microcalorimetry for the characterization of metal-based catalysts

As a highly promising clean energy source to replace fossil fuels in the 21st century, hydrogen energy has garnered considerable attention, with water electrolysis emerging as a key hydrogen production technology. The development of highly active and stable non-precious metal-based catalysts for the hydrogen evolution reaction (HER) is crucial for achieving efficient and low-cost hydrogen production through electrolysis. Recently, heterostructure composite catalysts comprising two or more non-precious metals have demonstrated outstanding catalytic performance. First, we introduced the basic mechanism of the HER and, based on the reported HER theory, discussed the essence of constructing heterostructures to improve the catalytic activity of non-noble metal-based catalysts, that is, the coupling effect between components effectively regulates the electronic structure and the position of d-band centers. Then three catalytic effects of non-precious metal-based heterogeneous catalysts are described: synergistic effect, electron transfer effect and support effect. Lastly, we emphasized the potential of non-precious metal-based heterogeneous catalysts to replace precious metal-based catalysts, and summarized the future prospects and challenges.

4 - Metal-free catalysts for hydrogen production

Aspects of aqueous foam stability in the presence of hydrocarbon oils and solid particles

Top – Scheme of the composite scintillator for registration of α-particles and γ-quanta. Bottom – Samples of the LuAG:Ce SCF/LuAG:Sc SC (a) and LuAG:Pr SCF/LuAG:Sc SC (b) composite scintillators prepared using the liquid phase epitaxy growth method.

Considering that there is a shortage of sustainable resources and that serious environmental issues need to be solved, the development of efficient catalysts has attracted a lot attention globally for energy saving and environmental improvement. In the last few decades, great progresses have been made in terms of fabrication and application of catalysts, however, systematic characterization with advanced technology and methods that enable researchers to have a detailed understanding of the catalysts’ properties and catalytic reactions, especially where an interface is present, are still limited. This Review focusses on the applications of advanced Scanning Probe Microscopy (SPM) and Spectroscopy techniques for the characterization of catalytic materials and their related reactions. A detailed description of advanced SPM and Spectroscopy techniques is introduced, followed by their applications in the characterization of surfaces and properties of common ordered catalytic materials including some coordination polymers and metal oxides. Various properties of these catalytic materials, such as conductivity, piezoelectricity, nanomechanics, photoresponse, and others, characterized by SPM and Spectroscopy are discussed. Subsequently, we introduce the high‐resolution imaging of chemical reactions and bond configuration by high‐resolution non‐contact Atomic Force Microscopy (NC‐AFM). Finally, the challenges involved in the development of SPM and Spectroscopy and an outlook for future research are presented. This Review provides fundamental insights into the characterization of heterogeneous catalysts and viewpoints to the development of smart catalytic materials.

ConspectusGraphene, a one-atom-thick layer of carbon with a honeycomb lattice, has drawn great attention due to its outstanding properties and its various applications in electronic and photonic devices. Mechanical exfoliation has been used for preparing graphene flakes (from monolayer to multilayer with thick pieces also typically present), but with sizes limited typically to less than millimeters, its usefulness is limited. Chemical vapor deposition (CVD) has been shown to be the most effective technique for the scalable preparation of graphene films with high quality and uniformity. To date, CVD growth of graphene on the most commonly used substrates (Cu and Ni foils) has been demonstrated and intensively studied. However, a survey of the existing literature and earlier work using Cu or Ni substrates for CVD growth indicates that the bilayer and multilayer graphene over a large area, particularly single crystals, have not been obtained.In this Account, we review current progress and development in the CVD growth of graphene and highlight the important challenges that need to be addressed, for example, how to achieve large single crystal graphene films with a controlled number of layers. A single-layer graphene film grown on polycrystalline Cu foil was first reported by our group, and since then various techniques have been devoted to achieving the fast growth of large-area graphene films with high quality. Commercially available Cu/Ni foils, sputtered Cu/Ni thin films, and polycrystalline Cu/Ni foils have been used for the CVD synthesis of bilayer, trilayer, and multilayer graphene. Cu/Ni alloy substrates are particularly interesting due to their greater carbon solubility than pure Cu substrates and this solubility can be finely controlled by changing the alloy composition. These substrates with controlled compositions have shown the potential for the growth of layer-tunable graphene films in addition to providing a much higher growth rate due to their stronger catalytic activity. However, the well-controlled preparation of single crystal graphene with a defined number of layers on Cu/Ni substrates is still challenging.Due to its small lattice mismatch with graphene, a single crystal Cu(111) foil has been shown to be an ideal substrate for the epitaxial growth of graphene. Our group has reported the synthesis of large-size single crystal Cu(111) foils by the contact-free annealing of commercial Cu foils, and single crystal Cu/Ni(111) alloy foils have also been obtained after the heat-treatment of Ni-coated Cu(111) foils. The use of these single crystal foils (especially the Cu/Ni alloy foils) as growth substrates has enabled the fast growth of single crystal single-layer graphene films. By increase of the Ni content, single crystal bilayer, trilayer, and even multilayer graphene films have been synthesized. In addition, we also discuss the wafer-scale growth of single-layer graphene on the single crystalline Cu/Ni(111) thin films.Recent research results on the large-scale preparation of single crystal graphene films with different numbers of layers on various types of Cu/Ni alloy substrates with different compositions are reviewed and discussed in detail. Despite the remarkable progress in this field, further challenges, such as the wafer-scale synthesis of single crystal graphene with a controlled number of layers and a deeper understanding of the growth mechanism of bilayer and multilayer graphene growth on Cu/Ni substrates, still need to be addressed.

We present new pieces of experimental findings on the self-assembling process of block copolymers (BCPs) on nonneutral solid substrate surfaces. The key to this event is the concurrent physisorption of preferred blocks and nonpreferred blocks on the surface. We uncover two different kinds of BCP chains adsorbed on the solid surface using an optimized solvent-rinsing approach. One is the inner strongly adsorbed BCP chains in which all constituent blocks lie flat and form a two-dimensional network-like structure regardless of their chain architectures, microdomain structures, and interfacial energetics. The other is outer "loosely adsorbed BCP chains," which form a poorly packed perpendicularly oriented microdomain structure on the substrate surface. The loosely adsorbed BCP chains act as seeds and promote poor perpendicularly oriented microdomains in a single BCP thin film. Interestingly, this substrate-field effect propagates into the film interior via chain entanglements between neighboring unadsorbed chains in the matrix and the loosely adsorbed chains up to a distance of ∼70 nm from the substrate surface. Finally, a new surface modification approach prevents the development of the undesirable substrate-field effect. We demonstrate that homopolymer chains composed of one of the constituent blocks adsorbed on the solid substrates act as a "structurally neutral" surface coating against both blocks.

Mircomeritics is a field of science that deals with small particles and that is applied especially in soil physics. In the realm of materials science, the accurate assessment of particle properties plays a pivotal role in shaping research, development, and industrial processes across diverse sectors. This comprehensive abstract explores the profound impact of various analytical techniques offered by Micromeritics, a pioneering scientific and technology company, on the understanding of particle behavior, quality control, and processing efficiency. The study commences with an exploration of Particle Size Analysis, a cornerstone technique that illuminates the distribution of particle sizes within a sample. With a primary emphasis on granularity, this methodology provides researchers and industries with invaluable insights into the physical characteristics of particulate matter. By unraveling particle size distribution, researchers can unravel the fundamental relationships between particle size and mechanical properties, such as rheology, and employ this knowledge for optimizing product design and manufacturing processes. Moreover, the technique's application extends to quality control, ensuring consistent product quality across batches. Surface Area Analysis, a companion technique, delves into the measurement of specific surface area—a parameter of paramount importance in understanding adsorption phenomena and catalytic activity. The method reveals the extent of available surface for interactions with gases, liquids, or other materials, facilitating the design of catalysts, adsorbents, and membranes with enhanced performance. In the context of catalytic processes, surface area information serves as a guiding star for designing efficient catalysts and tailoring reaction conditions. The exploration then delves into the intricate world of Pore Size and Volume Analysis. By characterizing the distribution and volume of pores within materials, researchers glean critical insights into adsorption behavior, porosity-related properties, and structural characteristics. This technique finds particular application in the characterization of adsorbents and catalysts, where pore architecture profoundly influences performance. Density and Porosity Measurement techniques further enrich the analytical arsenal. By accurately quantifying material density and porosity, researchers acquire a window into structural properties and performance. This information underpins the development of innovative materials tailored for specific applications—be it light-weight, high-strength structures or efficient energy storage materials. Chemisorption and Physisorption Analysis provide tools to investigate the complex interactions between materials and gases or liquids. By exploring adsorption phenomena on solid surfaces, researchers gain insights into molecular-level processes, aiding the design of materials for gas separation, purification, and catalysis.Mercury Intrusion Porosimetry offers a specialized approach to pore characterization. This method employs the intrusion of mercury into porous materials to elucidate pore size distribution and other related characteristics. It finds utility in diverse fields, ranging from geology to material science, where understanding pore structure is crucial for optimizing performance. Gas Adsorption Analysis techniques stand as sentinels at the interface of gas-solid interactions. By quantifying gas adsorption on solid surfaces, researchers unravel the intricate interplay between materials and gases. This knowledge informs the design of materials for applications like gas storage, separation, and heterogeneous catalysis. Powder Rheology enters the spotlight with its contribution to the assessment of powder flow and behavior. This technique is instrumental in guiding product design, processing optimization, and ensuring consistent product quality in the manufacturing industry. Material Density Determination techniques bring the focus back to fundamental material properties. Accurate density measurements are essential for understanding the packing and behavior of granular materials, influencing fields as diverse as construction materials, pharmaceuticals, and ceramics. Catalyst Characterization techniques present a specialized avenue of exploration. By analyzing surface area, pore size distribution, and catalytic activity, researchers glean critical insights into catalyst behavior. This knowledge is indispensable for optimizing catalytic processes and designing catalysts with enhanced efficiency.

A Study of the Thermal Reactions of Methyl Iodide Coadsorbed with Hydrogen on Ni(111) Surfaces: Hydrogenation of Methyl Species to Methane

Organic chemistry on solid surfaces

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 200 leading journals. To access a ChemInform Abstract, please click on HTML or PDF.

Open AccessCCS ChemistryRESEARCH ARTICLE1 Oct 2021Synergistic Effect of Platinum Single Atoms and Nanoclusters Boosting Electrocatalytic Hydrogen Evolution Yihui Zhu†, Pengfei Tian†, Hongliang Jiang, Jingren Mu, Lu Meng, Xiaozhi Su, Yu Wang, Yunxiang Lin, Yihua Zhu, Li Song and Chunzhong Li Yihui Zhu† Key Laboratory for Ultrafine Materials of Ministry of Education, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237 Shanghai Engineering Research Center of Hierarchical Nanomaterials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 , Pengfei Tian† Key Laboratory for Ultrafine Materials of Ministry of Education, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237 , Hongliang Jiang *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Key Laboratory for Ultrafine Materials of Ministry of Education, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237 , Jingren Mu Shanghai Engineering Research Center of Hierarchical Nanomaterials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 , Lu Meng Shanghai Engineering Research Center of Hierarchical Nanomaterials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 , Xiaozhi Su Shanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210 , Yu Wang Shanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201210 , Yunxiang Lin National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029 , Yihua Zhu Shanghai Engineering Research Center of Hierarchical Nanomaterials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 , Li Song National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029 and Chunzhong Li *Corresponding authors: E-mail Address: [email protected] E-mail Address: [email protected] Key Laboratory for Ultrafine Materials of Ministry of Education, School of Chemical Engineering, East China University of Science and Technology, Shanghai 200237 Shanghai Engineering Research Center of Hierarchical Nanomaterials, School of Materials Science and Engineering, East China University of Science and Technology, Shanghai 200237 https://doi.org/10.31635/ccschem.020.202000497 SectionsSupplemental MaterialAboutAbstractPDF ToolsAdd to favoritesDownload CitationsTrack Citations ShareFacebookTwitterLinked InEmail Maximizing atomic utilization of precious metal-based catalysts is of great significance in heterogeneous catalysis, also becoming a useful strategy to develop efficient electrocatalysts for hydrogen evolution reaction (HER). Although the dispersion of platinum (Pt) as single atoms (SAs) has increasingly been used in the design of HER electrocatalysts, it is still controversial if the SAs possess higher reactivity relative to the nanoparticles with identical atom loading. Here, by virtue of computational studies, we find that atomic step-rich Pt clusters and defective graphene (DG)-loaded Pt SAs are beneficial to water dissociation and hydrogen coupling, respectively, predicting that decent activity and high atomic utilization for alkaline HER electrocatalysis will be exhibited on the structure that integrates both Pt SAs and nanoclusters onto the DG matrix (PtSA/NC-DG). We experimentally synthesize the PtSA/NC-DG catalyst for alkaline HER. The optimized PtSA/NC-DG delivers an overpotential of 41 mV at a current density of 10 mA cm−2 and mass activity of 5.4 mA μgpt−1 at the overpotential of 100 mV. The mass activity is nearly 6 and 10 times higher than that of its Pt SA counterpart and commercial Pt/C catalyst. This work deepens the knowledge of the synergistic effect of single atoms and nanoclusters for alkaline HER electrocatalysis. Download figure Download PowerPoint Introduction Hydrogen production enabled by electrocatalytic methods represents an attractive approach to utilize renewable electricity from intermittent energy, such as solar, wind energy, geothermal power, and so forth.1–5 Although nonprecious materials based on earth's abundant resources have achieved substantial development,6–8 platinum (Pt) is still the benchmark catalyst for the electrocatalytic hydrogen evolution reaction (HER) in terms of low overpotentials and high mass activities.9–11 The electrocatalytic hydrogen production in alkaline electrolytes offers more benign conditions compared with that of acid media.12 More importantly, alkaline water splitting into hydrogen allows the application of active catalysts based on earth-abundant transition metals for anodic oxygen evolution reaction.1,6 However, the catalytic activity of Pt in alkaline media is nearly two to three orders of magnitude slower than that in acid media due to the high-energy barrier of water dissociation.13 In terms of cost efficiency, it is highly desirable to reduce the Pt amount to the greatest extent, while maintaining or even improving catalytic activities.14–17 In recent years, decreasing the size of catalytically active species in atomic dispersion, also referred to as single atoms (SAs), has attracted considerable attention thanks to their high atomic utilization and unique physicochemical properties.18–21 However, the catalytic nature remains highly controversial, especially since it is not clear how the SA sites achieve the splitting and recombination of chemical bonds.22,23 For instance, the hydrogen evolution process in alkaline media commonly consists of water dissociation and hydrogen coupling, a typical Volmer step (H2O + e− → H* + OH−) and Heyrovsky step (H2O + H* + e− → H2 + OH−) or Tafel step (H* + H* → H2).13 The structure with dual active components, typically a metal/oxide interfacial structure,24 has generally been adopted to optimize the water dissociation and hydrogen coupling simultaneously, boosting alkaline water electrolysis to produce hydrogen. To date, various attempts have successfully been made to obtain efficient low-Pt catalysts for acid HER electrocatalysis, but it has been determined that neither the Pt SAs nor nanoparticles deliver satisfactory performance in alkaline media.25–27 Developing efficient Pt-based catalysts with ultimate atomic utilization for alkaline HER electrocatalysis remains a severe challenge.28–31 Here, we demonstrate both theoretically and experimentally that the synergistic function from the integration of defective graphene (DG)-supported Pt SAs and nanoclusters (named as PtSA/NC-DG) boosted electrocatalytic hydrogen evolution in alkaline media. In alkaline HER, given typical elementary steps of the water dissociation and hydrogen coupling, we employed density functional theory (DFT) calculations to compute the two steps onto Pt(111), Pt(211), Pt38 cluster, and DG-supported Pt SA models. It was revealed that the Pt nanoclusters and SAs helped water dissociation and hydrogen coupling, respectively. Therefore, the coexistence of Pt SAs and nanoclusters on the DG matrix would decouple the optimization of the two steps, integrally delivering superior hydrogen evolution. We experimentally synthesized the PtSA/NC-DG and DG-supported Pt SAs (named as PtSA-DG). The electrocatalytic performance of the PtSA/NC-DG outperformed that of PtSA-DG and commercial Pt/C catalysts, verifying the synergistic effect of Pt SAs and nanoclusters for alkaline HER electrocatalysis. Experimental Methods Synthesis of DG About 20.00 g urea was dispersed uniformly in its crucible. Then the powder was calcined in a muffle furnace at 550 °C for 4 h, and the heating rate was controlled at 5 °C min−1. The temperature was reduced to 300 °C at 10 °C min−1, and then naturally cooled to obtain carbon nitride (C3N4). About 5.00 g of the prepared C3N4 and 4.50 g (C6H12O6 > 99 %) glucose were dispersed in mortar, the mixture was uniformly mixed, and then it was placed in a tube furnace at 1000 °C for 2 h under an argon atmosphere. The heating rate was controlled at 5 °C min−1. The temperature was reduced to 300 °C at 10 °C min−1, followed by natural cooling to obtain nitrogen-doped DG. Synthesis of PtSA-DG and PtSA/NC-DG In a typical preparation of Pt SAs loaded on the graphene matrix, 0.05 g of the DG was dispersed in 60.00 mL ultrapure water and sonicated for 30 min. Then 2.00 mL aqueous solution of chloroplatinic acid hexahydrate (2 mg mL−1) was added into the suspension and stirred for 12 h. The mixture was placed in an oil bath at 80 °C. It was collected by centrifuging, washing, and then drying at 75 °C for 6 h. The dark powdered sample, namely PtSA-DG, was obtained. The PtSA-DG was placed into a quartz tube and heated to 400 °C at a rate of 5 °C min−1 under a flow of gas mixture of argon and hydrogen (volume ratio = 9∶1). After 2 h of pyrolysis, the PtSA/NC-DG-400 was collected. By adjusting the annealing temperature (200 and 600 °C), the PtSA/NC-DG-X (X = 200 or 600) was also obtained. Other related experimental methods are available in the Supporting Information. Results and Discussion Structural investigation by DFT calculation The water dissociation and hydrogen coupling results on established models are shown in Figure 1 and Supporting Information Table S1. It was found that the energy barrier of water dissociation (EH2O) on a typical Pt(111) surface was estimated as 0.98 eV, and the hydrogen-binding energy (ΔGH*) was −0.20 eV, in keeping with previously published theoretical data.32,33 The results indicated the low ,activity of large size Pt crystals for alkaline HER electrocatalysis. When reducing the Pt size for the usage decrease, in addition to the thermodynamically stable Pt(111) surface, a high-index facet is increasingly exposed. Therefore, a typical high-index Pt(211) surface covered by atomic steps was here introduced.10 As shown in Figures 1a and 1b, the EH2O on the Pt(211) surface was 0.65 eV. On the contrary, the ΔGH* (−0.40 eV) on the Pt(211) surface was extremely negative (Figures 1c and 1d). The results suggested that the atomic steps can accelerate water dissociation to supply H*, but hamper the H* combination into H2. It can reasonably be anticipated that atom-assembled nanoclusters with rich atomic steps can further facilitate the water dissociation, but severely hinder the hydrogen coupling. The computational EH2O and ΔGH* on typical Pt38 clusters were 0.59 and −0.60 eV, respectively, verifying that only the presence of nanoclusters can not efficiently accomplish the water splitting into H2 (Figures 1b and 1d). In view of the ultimate in atomic utilization efficiency, Pt SAs anchored in suitable support naturally come to mind. Here, a nitrogen-doped defective carbon matrix for the anchoring of Pt SAs was considered, thanks to high structural feasibility and electronic conductivity as well as rich surface chemistry.34 Here, typical four-coordination structure is investigated in consideration of the high structure stability.10,32 It was determined that all simulated Pt-CxNy structures (x + y = 4) displayed large EH2O (Figure 1b), revealing the inferior water dissociation process. And moderate |ΔGH*| was exhibited on most of the Pt-CxNy structures, including Pt-C1N3, Pt-C2N2, and Pt-C4 (Figure 1d), thereby benefitting the hydrogen coupling process on these structures. Combined with the aim of atomic utilization maximization, these theoretical results predicted that decent activity and high atomic utilization of alkaline HER electrocatalysis would be exhibited on the structure that integrates both Pt SAs and nanoclusters onto proper nitrogen-doped defective carbon support. In the integrated structure, Pt clusters can accelerate water dissociation to supply adsorbed H atoms onto Pt clusters. The migration of H atoms from Pt clusters to the graphene support and then to the SAs can be carried out through hydrogen spillover.35–37 The DG as the substrate of Pt clusters receives excess H* from the spillover. Most of Pt-CxNy structures are beneficial to the hydrogen coupling process. Figure 1 | Structural investigation by DFT calculation. (a and c) The adsorption configurations of H2O and H on Pt(111), Pt(211), Pt38, and Pt-CxNy (x + y = 4), respectively. The dark blue, gray, blue, red, and white spheres are Pt, C, N, O, and H atoms, respectively. (b) Reaction energy diagram of water dissociation on Pt(111), Pt(211), Pt38, and Pt-CxNy (x + y = 4). (d) Free-energy barriers for HER on Pt(111), Pt(211), Pt38, and Pt-CxNy (x + y = 4). Download figure Download PowerPoint Synthesis and characterization of DG-supported Pt catalysts The nitrogen-doped DG selected for the loading of Pt species was obtained by the pyrolysis of the physical mixture of glucose and carbon nitride ( Supporting Information Figures S1 and S2). Transmission electron microscopy (TEM) images showed typical graphene nanosheets with a high degree of structural wrinkle38 ( Supporting Information Figure S3). The graphene displayed rich porosity and suitable pyridinic- or pyrrolic-nitrogen defects ( Supporting Information Figures S4 and S5), which were beneficial to the anchoring of metal species.39–41 The Pt SAs were anchored onto the DG matrix by a one-step electroless deposition to obtain the PtSA-DG with 3.89 wt % Pt loading.22,23 Aberration-corrected high-angle annular dark-field scanning TEM (HAADF-STEM) images showed the Pt species of the PtSA-DG were atomically dispersed onto the DG support20–22 (Figure 2a and Supporting Information Figure S6). Subjected to thermal treatment at a different temperature, the PtSA-DG was transformed into the PtSA/NC-DG-X (X = 200, 400, or 600 °C). In the thermal treatment, a part of the Pt SAs owing to its unsaturated coordination structure and low binding energy with CN matrix (Pt-CxNy, x + y < 4) were readily aggregated into Pt clusters.10,42 The Pt species in PtSA/NC-DG-X (X = 200, 400, or 600 °C ) dispersed as Pt nanoclusters with a similar average diameter ( Supporting Information Figure S7). Unless otherwise specified, the PtSA/NC-DG was the one obtained by heat treatment in 400 °C. From the HAADF-STEM images (Figure 2b and Supporting Information Figure S8), it was determined for the PtSA/NC-DG that both atom-assembled nanoclusters and SAs were dispersed onto the DG matrix. The energy-dispersive X-ray spectroscopy (EDS) mapping element further evidenced the coexistence of SAs and nanoclusters onto the nitrogen-doped carbon substrate (Figure 2c). X-ray diffraction (XRD) patterns (Figure 2d and Supporting Information S9) also revealed the presence and absence of crystalline Pt species in the PtSA/NC-DG and PtSA-DG, respectively. Figure 2 | Morphology and structure characterizations of PtSA-DG and PtSA/NC-DG. (a) High magnification HAADF-STEM image of PtSA-DG. (b) Gradually magnified HAADF-STEM images of PtSA/NC-DG. (c) Elemental mapping of PtSA/NC-DG. (d) XRD patterns of PtSA-DG and PtSA/NC-DG. Download figure Download PowerPoint X-ray absorption fine structure (XAFS) and X-ray photoelectron spectroscopy (XPS) measurements were carried out to identify the electronic and geometric structure of Pt species in the PtSA-DG and PtSA/NC-DG-X catalysts. The high-resolution Cl 2p XPS spectra showed the complete removal of chlorine ( Supporting Information Figure S10), suggesting the absence of Pt-Cl coordination in the obtained catalysts. The normalized X-ray absorption near-edge structure (XANES) spectra showed that white-line intensity of all the PtSA-DG and PtSA/NC-DG-X catalysts was located among PtO2 and Pt foil, demonstrating the existence of positively charged Pt species in these catalysts (Figure 3a).42 Furthermore, the decreased white-line intensity of PtSA/NC-DG-X catalysts indicated the enriching of Pt0 species with the increase of annealing temperature, which was also evidenced by high-resolution Pt 4f XPS spectra23 ( Supporting Information Figure S11). The coordination environments of Pt species were disclosed by k3-weighted extended XAFS (EXAFS). From Figure 3b and Supporting Information Figure S12, it was clearly found that only the dominant peak of Pt-C/N/O coordination was observed for the PtSA-DG catalyst, confirming the atomic dispersion of Pt species.22 For the PtSA/NC-DG-X catalysts, in addition to the peak from Pt-C/N/O contribution, those peaks close to the Pt–Pt coordination were also observed, evidencing the coexistence of Pt SAs and nanoclusters,10 in line with the above HAADF-STEM results. To more directly discriminate the coordination environment of PtSA-DG and PtSA/NC-DG catalysts, an EXAFS wavelet transform (WT) was performed (Figure 3c).43 For the PtSA-DG catalyst, only one intensity maximum region close to that of PtO2 was displayed, confirming the mononuclear centers of Pt species. Two maximum-intensity regions aligned with that of PtO2 and Pt foil were observed for the PtSA/NC-DG catalyst, strongly evidencing the presence of Pt-C/N/O and Pt–Pt coordination. Combining these spectroscopic results with the above microscopic observation, it was demonstrated that the PtSA-DG and PtSA/NC-DG were successfully constructed. Figure 3 | Spectroscopic identifications of PtSA-DG and PtSA/NC-DG-X. (a) Normalized XANES spectra and local enlargement at the Pt L3 edge. (b) k3-weighted R space Fourier-transformed spectra from the XANES. (c) WT for the EXAFS spectra. Download figure Download PowerPoint HER performance of different carbon-loaded Pt catalysts The high-performance catalytic activities of the PtSA/NC-DG for alkaline HER were verified in a typical three-electrode cell filled by 1 M KOH. First, from the polarization curves of PtSA/NC-DG-X catalysts ( Supporting Information Figure S13), the PtSA/NC-DG obtained at 400 °C was reactivity-optimized, probably due to the suitable ratio of Pt SAs and nanoclusters.32 The optimized PtSA/NC-DG achieved an overpotential (η) of 41 mV at a current density of 10 mA cm−2, significantly surpassing that of the PtSA-DG and commercial 20 wt % Pt/C catalysts (Figure 4a and Supporting Information Figure S14). The comparison of mass activities for precious metal-based catalysts is of great importance.9,44 Thus, the mass activities of PtSA-DG, PtSA/NC-DG, and commercial Pt/C were calculated based on the Pt loading at the electrode. The PtSA/NC-DG delivered significantly higher mass activity than the PtSA-DG and commercial Pt/C (Figure 4b and Supporting Information Figure S15). In particular, the mass activity of PtSA/NC-DG was as high as 5.40 mA μgpt−1 at 100 mV, which was nearly 6 and 10 times higher than that of PtSA-DG (0.83 mA μgpt−1) and commercial Pt/C (0.52 mA μgpt−1). In addition, the calculated turnover frequency (TOF) also demonstrated the remarkable activity of the PtSA/NC-DG ( Supporting Information Figure S16). From Supporting Information Figure S17, the Tafel slope of PtSA/NC-DG (40 mV dec−1) was close to that of commercial Pt/C, and was lower than that of PtSA-DG, following the Volmer–Tafel mechanism.28,45 Moreover, the exchange current density of PtSA/NC-DG was 1.25 mA cm−2 (Figure 4c), which is nearly seven and two times larger than that of PtSA-DG and commercial Pt/C, indicating rapid reaction kinetics of the PtSA/NC-DG. To further compare the intrinsic activity, the electrochemically active surface area (ECSA) was evaluated ( Supporting Information Figure S18). The ECSA-normalized mass activity of the PtSA/NC-DG at 100 mV was still five times higher than that of the PtSA-DG ( Supporting Information Figure S19), demonstrating superior intrinsic activity. To rule out the possible influence of particle size, exposed surface and the metal–support interaction, we prepared the Pt nanoclusters supported on high-surface-area carbon black support (PtNC-BP2000-400) with similar Pt loading according to previous studies.10 The PtNC-BP2000-400 without Pt SAs displayed a similar size of Pt clusters with PtSA/NC-DG ( Supporting Information Figure S20), which was also confirmed by high-resolution Pt 4f XPS spectra ( Supporting Information Figure S21). The metal–support interaction result from particle size could also be excluded. Then, we compared their electrocatalytic activity and stability. The PtSA/NC-DG catalyst displayed a lower overpotential and superior stability than PtNC-BP2000-400 ( Supporting Information Figure S22). The negligible overpotential increase after accelerated degradation test evidenced the long-term stability of PtSA-DG and PtSA/NC-DG, probably thanks to the confinement effect of the defective carbon matrix (Figure 4d and Supporting Information Figures S23 and S24).22,46 HAADF-STEM images of PtSA/NC-DG after 10,000 cycles further confirmed that PtSA/NC-DG is only slight larger than that of slight larger than that of the pristine PtSA/NC-DG ( Supporting Information Figure S25). N 1s and Pt 4f high-resolution XPS spectrum of PtSA/NC-DG further demonstrated the outstanding structural stability of PtSA/NC-DG catalyst ( Supporting Information Figures S26 and S27). The PtSA/NC-DG compared with that of PtSA-DG, PtNC-BP2000-400, commercial Pt/C as well as other Pt-based catalysts ( Supporting Information Table S2) displayed higher activity, verified the above theoretical synergistic effect of Pt SAs and nanoclusters boosting water splitting into hydrogen. Figure 4 | Electrochemical characterization. All data are IR-corrected. (a) LSV curves of PtSA-DG, PtSA/NC-DG, and commercial Pt/C in 1 M KOH. (b) Mass activities of PtSA-DG, PtSA/NC-DG, and commercial Pt/C at an overpotential of 50 and 100 mV. (c) Exchange current density of PtSA-DG, PtSA/NC-DG, and commercial Pt/C. (d) LSV curves of PtSA/NC-DG recorded initially and after 10,000 potential cycles. IR, infrared; LSV, linear sweep voltammetry. Download figure Download PowerPoint Conclusion Combining the DFT simulation and experimental verification, we have reported a highly efficient PtSA/NC-DG electrocatalyst for alkaline HER by the integration of Pt nanoclusters and SAs onto DG matrix. In the integrated structure, the Pt nanoclusters promote water dissociation into *H and *OH, and the Pt SAs facilitate the H–H coupling into gaseous hydrogen. Consequently, despite low Pt loading in the PtSA/NC-DG catalyst, the electrocatalytic performance toward alkaline HER is substantially better than that of the Pt SA counterpart and commercial Pt/C catalyst with 20 wt % Pt. The notion presented in this work will provide some guidance for the design of noble metal-based heterogeneous catalysts approaching the ultimate in atomic utilization efficiency. Supporting Information Supporting Information is available. Conflict of Interest There is no conflict of interest to report. Funding Information This work was supported by the National Natural Science Foundation of China (nos. 21838003, 91834301, and 21978278), the Shanghai Scientific and Technological Innovation Project (nos. 18JC1410500 and 19JC1410400), and the Fundamental Research Funds for the Central Universities (no. 222201718002). Acknowledgments The authors thank Shanghai Synchrotron Radiation Facility (BL14W1, SSRF).

The production of single crystal diamond thin films of large area would be a technological breakthrough for a variety of electronic and optical applications. In terms of the objectives of this contract, single crystal films would produce high quality doped regions and thus better barriers for energy conversion in the vacuum ultraviolet. To date, diamond single crystal films have been made homo-epitaxially on natural or synthetic diamond single crystals. As large single crystal diamond is prohibitively expensive, there is a need to find matching substrates for diamond heteropolarities. Cubic boron nitride has the diamond lattice structure and matches nearly perfectly the cell dimensions. However, large area cubic BN single crystal substrates are not available, as c-BN is stable, just like diamond, at high pressures and high temperatures only. The widely used Si substrates have a large lattice constant mismatch with diamond.

In part II of this series, it was reported that the solar home system (SHS) supplied by REB in some islands of the Meghna river in the district of Narsingdi could not meet the demand of the recipients in the rainy season when the sky remained overcast with cloud. The tilt angle for all installations was 45° facing south. In this study, effects of direct and diffuse sunlight with variation of tilt angles from 0° to 45° were studied using a mono crystalline silicon cell. Pyranometer and the solar panel were kept under identical conditions. Energy absorbed by the solar panel in diffuse sunlight was found 0.55% of that received by the Pyranometer under similar conditions showing that mono crystalline silicon solar cell of the type under study was not suitable for use in SHS. Moreover, the gap between the panel and the solid surface below it has significant effects on the efficiency of the solar cell. Further similar study using different kinds of cells- mono crystalline, poly crystalline and amorphous is needed for proper designs of SHS. Optimization of the gap between the panel and the solid surface below it is important for roof-mounted and ground-mounted panels. Key words: Silicon solar cells; Tilt angle; Diffuse light; Home lighting; Monocrystaline. DOI: http://dx.doi.org/10.3329/bjsir.v46i1.8114 Bangladesh J. Sci. Ind. Res. 46(1), 117-122, 2011

γ-Valerolactone (GVL) is a value-added renewable chemical with great potential and can be obtained from biomass by the hydrogenation of levulinic acid (LA) using metal-based catalysts, such as Ru/TiO2. We here report an in depth study of the effect of catalyst synthesis parameters on the performance of Ru/TiO2 (anatase), varying the nature of the Ru-precursor and the conditions of the calcination and/or reduction step. Catalyst performance was evaluated under batch conditions at a hydrogen pressure of 45bar and using either water (90°C) or dioxane (150°C) as solvent. The experiments showed that catalyst activity depends greatly on the Ru precursor used (RuCl3, RuNO(NO3)3, Ru(NH3)6Cl3). Best results when considering the turn-over frequencies (TOF) of the catalysts were obtained using the RuNO(NO3)3 precursor, whereas RuCl3 performed better when considering the initial rate based on Ru intake. An intermediate calcination step and the use of a hydrogen-rich sweep gas during the final reduction step were shown to have a negative impact on catalyst activity. Characterization of the fresh catalysts by BET and TEM provided valuable insight in the relation between the catalyst structure and its activity.