Search

Thermoelectric devices enable direct conversion between thermal and electrical energy. Recent studies have indicated that the thin film/substrate heterostructure is effective in achieving high thermoelectric performance via decoupling the Seebeck coefficient and electrical conductivity otherwise adversely inter-dependent in homogenous bulk materials. However, the mechanism underlying the thin film/substrate heterostructure thermoelectricity remains unclear. In addition, the power output of the thin film/substrate heterostructure is limited to the nanowatt scale to date, falling short of the practical application requirement. Here, we fabricated the CrN/SrTiO3−x heterostructures with high thermoelectric output power and outstanding thermal stability. By varying the CrN film thickness and the reduction degree of SrTiO3−x substrate, the optimized power output and the power density have respectively reached 276 μW and 108 mW/cm2 for the 30 nm CrN film on a highly reduced surface of SrTiO3−x under a temperature difference of 300 K. The performance enhancement is attributed to the CrN/SrTiO3−x heterointerface, corroborated by the band bending as revealed by the scanning Kelvin probe microscopy. These results will stimulate further research efforts towards interface thermoelectrics.

Sustainable methanol production via CO2 hydrogenation leads to increased interest in the understanding of active phase of Cu/ZnO/Al2O3 (CZA) catalyst. Model catalysts of ZnO/Cu(111) with structures varied from two-dimensional planar to three-dimensional nanoparticles were prepared by atomic layer deposition (ALD) method. By combing scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS) at near-ambient pressure of CO2 hydrogenation, we reveal that the submonolayer ZnO/Cu(111) transformed into Cu-Zn alloy under 10 mbar CO2/H2 at 493 K, and underwent a partial re-oxidation during evacuation. The dynamic phase transformation of ZnO/Cu(111) may partly explain the existence of differences and apparently contradictory theories to account for the origin of active phase in CZA catalysts.

Microscale electrochemical energy storage devices, e.g., micro-supercapacitors (MSCs), possessing tailored performance and diversified form factors of lightweight, miniaturization, flexibility and exceptional integration are highly necessary for the smart power sources-unitized electronics. Despite the great progress, the fabrication of MSCs combining high integration with high volumetric performance remains largely unsolved. Herein, we develop a simple, fast and scalable strategy to fabricate graphene based highly integrated MSCs by a new effective continuous centrifugal coating technique. Notably, the resulting highly conductive graphene films can act as not only patterned microelectrodes but also metal-free current collectors and interconnects, endowing modular MSCs with high integrity, remarkable flexibility, tailored voltage and capacitance output, and outstanding performance uniformity. More importantly, the strong centrifugal force and shear force generated in continuous centrifugal coating process lead to graphene films with high alignment, compactness and packing density, contributing to excellent volumetric capacitance of ~31.8 F cm−3 and volumetric energy density of ~2.8 mWh cm−3, exceeding most reported integrated MSCs. Therefore, our work paves a novel way for simple and scalable fabrication of integrated MSCs and offers promising opportunities as standalone microscale power sources for new-generation electronics.

Non-oxidative conversion of methane to olefins, aromatics and hydrogen (MTOAH) has been reported recently over metal single sites such as iron and platinum. The reaction was proposed to involve catalytic activation of methane followed by gas phase C−C coupling of methyl radicals. This study using H atom Rydberg Tagging time-of-flight technique provides direct experimental evidence for the formation of hydrogen radicals during MTOAH reaction over a catalytic quartz wall reactor containing embedded iron species (denoted as Fe-reactor). Fe-reactor gives 7.3% methane conversion at 1273 K with 41.2% selectivity toward C2 (ethane, ethylene and acetylene) and 31.8% toward BTX (benzene, toluene and xylene), respectively. The enhancing effects of hydrogen radicals on overall MTOAH performance are validated by cofeeding hydrogen donor benzene, which provides an additional route of methane activation apart from catalytic activation.

Thermoelectric properties of orthorhombic or rhombohedral GeSe have attracted great attention recently, with the rise of its structural analog SnSe. However, the p-type cubic GeSe with higher symmetry and higher valence band degeneracy, which might exhibit higher thermoelectric performance, has never been synthesized. Here we report on the successful synthesis of p-type crystalline cubic GeSe by alloying with Sb2Te3 and the spontaneously formed Ge-vacancies. An unexpected glass-like temperature independent lattice thermal conductivity is observed in crystalline cubic GeSe, which results from strong phonon scattering by vacancy-induced disorders. Combining the multiple scattering theory and chemical bond analysis, we further reveal the existence of Anderson localization induced by Ge-vacancies. The Anderson localization results in a nearly constant Seebeck coefficient with increasing the carrier concentration. These results provide a general insight towards understanding and improving the thermoelectric properties of thermoelectric materials with vacancies and atomic-scale disorders.

The effect of the Al2O3 structure on the performance of Pt/Ga/Al2O3 catalysts is investigated for the direct dehydrogenation of propane. The study unveils that the structure of Al3+ determines the bulk structure of catalysts, particularly a high content of coordinatively unsaturated Al3+ sites (penta-coordinated Al3+, denoted as Al3+penta) could lead to a remarkably improved dehydrogenation activity of the catalyst. The bulk characterization reveals that the sufficient amount of Al3+penta in Al2O3 benefit the dispersion of Pt and Ga2O3 on the Al2O3 support. At the same time, TPR results reveal that the presence of Pt facilitates the reduction of Ga2O3, likely due to the hydrogen spillover between the well dispersed Pt and Ga2O3, which consequently enhances the synergistic function between Pt and Ga2O3 in the dehydrogenation of propane. Recyclability tests demonstrate that the dehydrogenation activity stabilizes after three cycles over the Pt/Ga/Al2O3 catalyst.

Oxide-Zeolite (OX-ZEO) bifunctional catalyst design concept has been exemplified in several processes to direct conversion syngas to value-added chemicals and fuels such as mixed light olefins, ethylene, aromatics and gasoline. Herein we demonstrate that the product can be steered toward liquefied petroleum gas (LPG) with a selectivity up to 89% in hydrocarbons especially propane selectivity reaching 80% at CO conversion of 63% using ZnCrOx-H-SSZ-39 catalyst. Interestingly, the quantity of the acid sites of SSZ-39 does not influence obviously the hydrocarbon distribution but the strength is crucial for selective formation of propane. This finding provides an alternative route of LPG synthesis from a variety of carbon resources via syngas.

Gold, as the common current collector in solid oxide electrolysis cell (SOEC), is traditionally considered to be inert for oxygen evolution reaction at the anode of SOEC. Herein, gold nanoparticles were loaded onto conventional strontium doped lanthanum manganite-yttria stabilized zirconia (LSM-YSZ) anode, which evidently improved the performance of oxygen evolution reaction at 800 °C. The current densities at 1.2 V and 1.4 V increased by 60.0% and 46.9%, respectively, after loading gold nanoparticles onto the LSM-YSZ anode. Physicochemical characterizations and electrochemical measurements suggested that the improved SOEC performance was attributed to the accelerated electron transfer of elementary process in anodic polarization reaction and the newly generated triple phase boundaries in gold nanoparticles-loaded LSM-YSZ anode.

Aromatics are important basic chemicals. However, direct conversion of syngas via the conventional Fischer-Tropsch synthesis produces little aromatics. We presented herein that a bifunctional composite of ZSM-5 in combination with ZnCrOx catalyzes syngas conversion to aromatics. Particularly, ZSM-5 crystals with a sheet-like morphology can enhance significantly the aromatization activity. The lower length ratio of the b/a axes of the crystals, the more aromatics form but without influencing the selectivity of small molecules such as CH4 and C2–C4. Since the acid properties and the Al chemical environment were not altered while the morphology changed, the enhanced aromatic selectivity is likely attributed to the favored diffusion of aromatics in these sheet-like crystals.

Solid oxide electrolysis cell (SOEC) can electrochemically convert CO2 to CO at the gas-solid interface with a high current density and Faradaic efficiency, which has attracted increasing attentions in recent years. Exploring efficient catalyst for electrochemical CO2 reduction reaction (CO2RR) at the cathode is a grand challenge for the research and development of SOEC. Sr2Fe1.5Mo0.5O6-δ (SFM) is one kind of promising cathode materials for SOEC, but suffers from insufficient activity for CO2RR. Herein, Gd0.2Ce0.8O1.9 (GDC) nanoparticles were infiltrated onto the SFM surface to construct a composite GDC-SFM cathode and improve the CO2RR performance in SOEC. The current density over the GDC infiltrated SFM cathode with a GDC loading of 12.8 wt% reaches 0.446 A cm−2 at 1.6 V and 800 °C, which is much higher than that over the SFM cathode (0.283 A cm−2). Temperature-programmed desorption of CO2 measurements suggest that the infiltration of GDC nanoparticles significantly increases the density of surface active sites and three phase boundaries (TPBs), which are beneficial for CO2 adsorption and subsequent conversion. Electrochemical impedance spectroscopy results indicate that the polarization resistance of 12.8 wt% GDC-SFM cathode was obviously decreased from 0.46 to 0.30 Ω cm2 after the infiltration of GDC nanoparticles.

Boron had been introduced into the structure of carbon material (BC), which was used as the support of Pd catalyst for hydrogenation of 4-carboxybenzaldehyde (4-CBA). The physical properties and chemical composition of the support and corresponding catalyst were characterized by N2 adsorption–desorption, Raman spectroscopy, inductively coupled plasma optical emission spectroscopy (ICP-OES), element analysis (EA), high-resolution transmission electron microscopy (HRTEM), CO-pulse chemisorption and X-ray photoelectron spectroscopy (XPS). The results demonstrate that Pd/BC catalyst exhibits a superior activity and good stability due to the more uniform dispersion of Pd nanoparticles, the presence of mesoporous structure and the enhanced interaction between Pd nanoparticles and the support, compared to carbon and N-doped carbon supported Pd catalysts (Pd/C and Pd/NC, respectively).

Carbon nanotubes (CNTs) have shown as unique nanoreactors to tune the catalytic activity of confined nano-catalysts. Here we report that the catalytic performance of molybdenum carbide nanoparticles (MoCx NPs) for the hydrogen evolution reaction (HER) process can be enhanced by encapsulation within single-walled carbon nanotubes (SWNTs) with a diameter of 1-2 nm. The catalyst with MoCx NPs located on the interior surface of SWNTs (MoCx@SWNTs) exhibits a lower onset over-potential and a smaller Tafel slope than the one with MoCx NPs attached on the exterior surface (MoCx/SWNTs). This is likely attributed to the much smaller particle size and the more reduced states of the confined MoCx NPs, as well as the larger specific surface area of MoCx@SWNTs compared with MoCx/SWNTs. In addition, the electronic structure of the confined MoCx NPs might be modified by the confinement effects of SWNTs, and hence the adsorption free energy of H atoms on the confined MoCx NPs, which could also contribute to their higher performance. These results suggest that the SWNTs can be further explored for constructing novel catalysts with beneficial catalytic performance.

Nitrogen doping has been proved to be an effective way to modify the properties of graphene and other carbon materials. Herein, we explore a composite with nitrogen doped carbon overlayers wrapping SiC substrate as a support for Ni (Ni/CN-SiC) and evaluate its effects on the methanation activity. The results show that both the activity and stability of Ni are enhanced. Characterization with STEM, XRD, XPS, Raman and H2-TPR indicates that nitrogen doping generates more defects in the carbon overlayers, which benefit the dispersion of Ni. Furthermore, the reduction of Ni is facilitated.

Supercapacitors, with ultrahigh power density, superior rate capability, long-term cyclability, and exceptional safety, are regarded as one highly competitive candidate of electrochemical energy storage devices, filling the gap between batteries and conventional capacitors. Despite of tremendous effort, elaborated screening of high-performance electrode materials, e.g., graphene, is still intensively required. In this review, we describe the most recent progress in the research and development of graphene-based materials for high-performance and new-concept supercapacitors for the targeted applications in next-generation and smart electronics. First, the design and fabrication of high-performance supercapacitors, including electrical double layer capacitors, pseudocapacitors and hybrid supercapacitors, were summarized in term of the charge storage mechanism. Second, new-concept supercapacitors with multiple functionalities of high-voltage, fiber-shape, microscale and shape-diversity in order to fulfill the requirements of future electronics are reviewed. Accordingly, special emphasis is given to the structure-dependent-performance effects of pores, hybridization, dimensionalities of graphene-based materials on performance of supercapacitors, and tremendous potential of graphene-based planar micro-supercapacitors for the direct seamlessly integration with versatile micro-electronics. Finally, perspectives and challenges of graphene-based supercapacitors are briefly discussed.

Zeolitic imidazolate frameworks (ZIFs) are widely employed in catalyst synthesis as parental materials for electrochemical energy storage and conversion. Herein, we have demonstrated a facile synthesis of highly efficient catalyst for oxygen reduction reaction in both alkaline and acidic medium, which is derived from ZIF-8 functionalized with ammonium ferric citrate via two-step pyrolysis in Ar and NH3 atmosphere. The results reveal that the catalytic activity improvement after NH3 pyrolysis benefits from mesopore-dominated morphology and high utilization of Fe-containing active sites. The optimum catalyst shows excellent performance in zinc-air battery and polymer electrolyte membrane fuel cell tests.

Nitrogen-doped carbon materials encapsulating 3d transition metals are promising alternatives to replace noble metal Pt catalysts for efficiently catalyzing the oxygen reduction reaction (ORR). Herein, we use cobalt substituted perfluorosulfonic acid/polytetrafluoroethylene copolymer and dicyandiamide as the pyrolysis precursor to synthesize nitrogen-doped carbon nanotube (N CNT) encapsulating cobalt nanoparticles hybrid material. The carbon layers and specific surface area of N CNT have a critical role to the ORR performance due to the exposed active sites, determined by the mass ratio of the two precursors. The optimum hybrid material exhibits high ORR activity and stability, as well as excellent performance and durability in zinc–air battery.

Co-electrolysis of CO 2 and H 2 O using high-temperature solid oxide electrolysis cells (SOECs) into valuable chemicals has attracted great attentions recently due to the high conversion and energy efficiency, which provides opportunities of reducing CO 2 emission, mitigating global warming and storing intermittent renewable energies. A single SOEC typically consists of an ion conducting electrolyte, an anode and a cathode where the co-electrolysis reaction takes place. The high operating temperature and difficult activated carbon–oxygen double-bond of CO 2 put forward strict requirements for SOEC cathode. Great efforts are being devoted to develop suitable cathode materials with high catalytic activity and excellent long-term stability for CO 2 /H 2 O electro-reduction. The so far cathode material development is the key point of this review and alternative strategies of high-performance cathode material preparation is proposed. Understanding the mechanism of CO 2 /H 2 O electro-reduction is beneficial to highly active cathode design and optimization. Thus the possible reaction mechanism is also discussed. Especially, a method in combination with electrochemical impedance spectroscopy (EIS) measurement, distribution functions of relaxation times (DRT) calculation, complex nonlinear least square (CNLS) fitting and operando ambient pressure X-ray photoelectron spectroscopy (APXPS) characterization is introduced to correctly disclose the reaction mechanism of CO 2 /H 2 O co-electrolysis. Finally, different reaction modes of the CO 2 /H 2 O co-electrolysis in SOECs are summarized to offer new strategies to enhance the CO 2 conversion. Otherwise, developing SOECs operating at 300–600 °C can integrate the electrochemical reduction and the Fischer–Tropsch reaction to convert the CO 2 /H 2 O into more valuable chemicals, which will be a new research direction in the future.

The adsorption of CO on Pt group metals, as a most fundamental elementary reaction step, has been widely studied in catalysis and electrocatalysis. Particularly, the structures of CO on Pt(111) have been extensively investigated, owing to its importance to both fundamental and applied catalysis. Yet, much less is known regarding CO adsorption on a Pt(111) surface modulated by supported oxide nanostructures, which is of more relevance to technical catalysis. We thus investigated the coverage-dependent adsorption of CO on a Pt(111) surface partially covered by FeOx nanostructures, which has been demonstrated as a remarkable catalyst for low-temperature CO oxidation. We found that, due to its strong chemisorption, the coverage-dependent structure of CO on bare Pt is not influenced by the presence of FeOx. But, oxygen-terminated FeOx nanostructures could modulate the diffusivity of CO at their vicinity, and thus affect the formation of ordered CO superstructures at low temperatures. Using scanning tunneling microscopy (STM), we inspected the diffusivity of CO, followed the phase transitions of CO domains, and resolved the molecular details of the coverage-dependent CO structures. Our results provide a full picture for CO adsorption on a Pt(111) surface modulated by oxide nanostructures and shed lights on the inter-adsorbate interaction on metal surfaces.

The effects of the acid site in main channels of MOR zeolites on their product selectivity and deactivation in the MTO (methanol to olefin) reactions were investigated. The catalytic analysis demonstrates that the pyridine modified MOR zeolite yielded high selectivity (> 65.3%) of C2=-C4=, although the conversion dropped from 100% to 54%. Furthermore, both the catalytic lifetime of MOR and the stability of yielding the lower olefins were increased from less than 30 min to more than 120 min after the modification with pyridine. 1H MAS NMR on MOR and modified MOR shows that the acid sites in main channel do not benefit the productivity of lower olefins and catalysts lifetime. It can be concluded from ex-situ 13C CP MAS NMR that the deposit species during the MTO reaction depend on the pore sizes, and the formation of large alkyl aromatic species more likely occurs in the 12-ring main channels rather than the 8-ring side pocket.

Rechargeable lithium-oxygen (Li–O2) batteries have been considered as the most promising candidates for energy storage and conversion devices because of their ultra high energy density. Until now, the critical scientific challenges facing Li–O2 batteries are the absence of advanced electrode architectures and highly efficient electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), which seriously hinder the commercialization of this technology. In the last few years, a number of strategies have been devoted to exploring new catalysts with novel structures to enhance the battery performance. Among various of oxygen electrode catalysts, carbon-based materials have triggered tremendous attention as suitable cathode catalysts for Li–O2 batteries due to the reasonable structures and the balance of catalytic activity, durability and cost. In this review, we summarize the recent advances and basic understandings related to the carbon-based oxygen electrode catalytic materials, including nanostructured carbon materials (one-dimensional (1D) carbon nanotubes and carbon nanofibers, 2D graphene nanosheets, 3D hierarchical architectures and their doped structures), and metal/metal oxide-nanocarbon hybrid materials (nanocarbon supporting metal/metal oxide and nanocarbon encapsulating metal/metal oxide). Finally, several key points and research directions of the future design for highly efficient catalysts for practical Li–O2 batteries are proposed based on the fundamental understandings and achievements of this battery field.

Replacing platinum for catalyzing hydrogen evolution reaction (HER) in acidic medium remains great challenges. Herein, we prepared few-layered MoS2 by ball milling as an efficient catalyst for HER in acidic medium. The activity of as-prepared MoS2 had a strong dependence on the ball milling time. Furthermore, Ketjen Black EC 300J was added into the ball-milled MoS2 followed by a second ball milling, and the resultant MoS2/carbon black hybrid material showed a much higher HER activity than MoS2 and carbon black alone. The enhanced activity of the MoS2/carbon black hybrid material was attributed to the increased abundance of catalytic edge sites of MoS2 and excellent electrical coupling to the underlying carbon network.

Long-term stability test of Mo/HZSM-5-N catalysts (HZSM-5-N stands for nano-sized HZSM-5) in methane dehydroaromatization (MDA) reaction has been performed with periodic CH 4 -H 2 switch at 1033–1073 K for more than 1000 h. During this test, methane conversion ranges from 13% to 16%, and mean yield to aromatics (i.e. benzene and naphthalene) exceeds 10%. N2-physisorption, XRD, NMR and TPO measurements were performed for the used Mo/HZSM-5 catalysts and coke deposition, and the results revealed that the periodic hydrogenation can effectively suppress coke deposition by removing the inert aromatic-type coke, thus ensuring Mo/HZSM-5 partly maintained its activity even in the presence of large amount of coke deposition. The effect of zeolite particle size on the catalytic activity was also explored, and the results showed that the nano-sized zeolite with low diffusion resistance performed better. It is recognized that the size effect was enhanced by reaction time, and it became more remarkable in a long-term MDA reaction even at a low space velocity.

Carbon dioxide transformation to fuels or chemicals provides an attractive approach for its utilization as feedstock and its emission reduction. Herein, we report a gas-phase electrocatalytic reduction of CO 2 in an electrolytic cell, constructed using phosphoric acid-doped polybenzimidazole (PBI) membrane, which allowed operation at 170 °C. Pt/C and PtMo/C with variable ratio of Pt/Mo were studied as the cathode catalysts. The results showed that PtMo/C catalysts significantly enhanced CO formation and inhibited CH 4 formation compared with Pt/C catalyst. Characterization by X-ray diffraction, X-ray photoelectron spectroscopy and transmission electron microscopy revealed that most Mo species existed as MoO 3 in PtMo/C catalysts and the interaction between Pt and MoO x was likely responsible for the enhanced CO formation rate although these bicomponent catalysts in general had a larger particle size than Pt/C catalyst.

Commercial production of vinyl chloride from acetylene relies on the use of HgCl2 as the catalyst, which has caused severe environmental problem and threats to human health because of its toxicity. Therefore, it is vital to explore alternative catalysts without mercury. We report here that N-doped carbon can catalyze directly transformation of acetylene to vinyl chloride. Particularly, N-doped high surface area mesoporous carbon exhibits a rather high activity with the acetylene conversion reaching 77% and vinyl chloride selectivity above 98% at a space velocity of 1.0 mL·min−1·g −1 and 200 °C. It delivers a stable performance within a test period of 100 h and no obvious deactivation is observed, demonstrating potentials to substitute the notoriously toxic mercuric chloride catalyst.

A versatile wet chemistry method is developed for filling of subnanometer sized metal particles in carbon nanotubes with a diameter smaller than 1.5 nm. As an example, we showed that a confined bi-component Pd-V catalyst exhibit a higher benzene hydroxylation activity compared with that within multi-walled carbon nanotubes.

Direct conversion of methane to benzene or other valuable chemicals is a very promising process for the efficient application of natural gas. Compared with conversion processes that require oxidants, non-oxidative direct conversion is more attractive due to high selectivity to the target product. In this paper, an alternative route for methane dehydrogenation and selective conversion to benzene and hydrogen without the participation of oxygen is discussed. A brief review of the catalysts used in methane dehydroaromatization (MDA) is first given, followed by our current understanding of the location and the active phase of Mo species, the reaction mechanism, the mechanism of carbonaceous deposit and the deactivation of Mo/zeolite catalysts are systematically discussed. Ways to improve the catalytic activity and stability are described in detail based on catalyst and reaction as well as reactor design. Future prospects for methane dehydroaromatization process are also presented.