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Diatomic catalysts, particularly those with heteronuclear active sites, have recently attracted considerable attention for their advantages over single-atom catalysts in reactions involving multielectron transfers. Herein, we report bimetallic iridium−iron diatomic catalysts (IrFe−N−C) derived from metal−organic frameworks in a facile wet chemical synthesis followed by postpyrolysis. We use various advanced characterization techniques to comprehensively confirm the atomic dispersion of Ir and Fe on the nitrogen-doped carbon support and the presence of atomic pairs. The asobtained IrFe−N−C shows substantially higher electrocatalytic performance for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) when compared to the single-atom counterparts (i.e., Ir−N−C and Fe−N−C), revealing favorable bifunctionality. Consequently, IrFe−N−C is used as an air cathode in zinc− air batteries, which display much better performance than the batteries containing commercial Pt/C + RuO2 benchmark catalysts. Our synchrotron-based X-ray absorption spectroscopy experiments and density functional theory (DFT) calculations suggest that the IrFe dual atoms presumably exist in an IrFeN6 configuration where both Ir and Fe coordinates with four N atoms and two N atoms are shared by the IrN4 and FeN4 moieties. Furthermore, the Fe site contributes mainly to the ORR, while the Ir site plays a more important role in the OER. The dual-atom sites work synergistically, reducing the energy barrier of the rate-determining step and eventually boosting the reversible oxygen electrocatalysis. The IrFe−N−C catalysts hold great potential for use in various electrochemical energy storage and conversion devices.

Soft oxidant, CO2, triggered the catalytic performance of propane dehydrogenation with balanced stability and selectivity.

Atomically dispersed catalysts (ADCs) have recently drawn considerable interest for use in water electrolysis to produce hydrogen, because they allow for maximal utilization of metal species, particularly the expensive and scarce platinum group metals. Herein, we report the electrocatalytic performance of atomically dispersed ruthenium catalysts (Ru ADCs) with ultralow Ru loading (0.2 wt%). The as-obtained Ru ADCs (Ru (0.2)-NC) are active for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), which only require a low overpotential (η) of 47.1 and 72.8 mV to deliver 10 mA cm for HER in 0.5 M HSO and 1.0 M KOH, respectively, and of 300 mV for OER in 1.0 M KOH, showing favorable bifunctionality. Density functional theory (DFT) calculations reveal that the Ru-N bonding plays an important role in lowering the energy barrier of the reactions, boosting the HER and OER activities. Furthermore, the bipolar membrane (BPM) water electrolysis using the bifunctional Ru (0.2)-NC as both HER and OER catalysts can afford 10 mA cm under a low cell voltage of only 0.89 V, and does not show any performance decay upon 100 h continuous operation, showing great potential for energy-saving hydrogen production., L. L. acknowledges the financial support from the National Innovation Agency of Portugal through the Mobilizador Programme (Baterias 2030, Grant No. POCI-01-0247-FEDER-046109). B. L. acknowledges the Natural Science Foundation of LiaoNing Province, China (Grant No. 20180510014) for funding. Z. P. Y. is grateful for the scholarship offered by the China Scholarship Council (Grant No. 201806150015). This work was also in part financially supported by: LA/P/0045/2020 (ALiCE), UIDB/50020/2020 and UIDP/50020/2020 (LSRE-LCM) funded by national funds through FCT/MCTES (PIDDAC); project 2DMAT4FUEL (POCI-01-0145-FEDER-029600 - COMPETE2020 – FCT/MCTES - PIDDAC, Portugal). In addition, this work was carried out in part through the use of the INL Advanced Electron Microscopy, Imaging and Spectroscopy (AEMIS) Facility.

HBr triggered the activities of catalytic propane dehydrogenation with balanced stability and selectivity.

Pt-based catalysts are widely used in propane dehydrogenation to meet the dramatically increased demand of propylene from an on-purpose catalytic process. Although the process has been commercializ...

Electrochemical reduction of CO2 (CERR) to value-added chemicals is an attractive strategy for greenhouse gas mitigation, and carbon recycles utilization. Conventional metal catalysts suffered from low durability and sluggish kinetics impede the practical application. On the other hand, doped carbon materials recently demonstrate superior catalytic performance in CERR, which shows the potential to diminish the problems of metal catalysts to some extent. Herein, we present the design and fabrication of nitrogen (N), phosphorus (P) co-doped metal-free carbon materials as an efficient and stable electrocatalyst for reduction of CO2 to CO, which exhibits an excellent performance with a high faradaic efficiency of 92% (−0.55 V vs. RHE) and up to 24 h stability. A series of characterizations including TEM and XPS verified that nitrogen and phosphorous are successfully incorporated into the carbon matrix. Moreover, the comparisons between co-doping and single doping catalysts reveal that co-doping can significantly increase CERR performance. The improved catalytic activity is attributed to the synergetic effects between nitrogen and phosphorous dopants, which effectively modulate properties of the active site. The density functional theory (DFT) calculations were also performed to understand the synergy effects of dopants. It is revealed that the phosphorous doping can significantly lower the Gibbs free energy of COOH* formation. Moreover, the introduction of the second dopants phosphorous can reduce the reaction barrier along the reaction path and cause polarization of density of states at the Fermi level. These changes can greatly enhance the activity of the catalysts. From a combined experimental and computational exploration, current work provides valuable insights into the reaction mechanism of CERR on N, P co-doped carbon catalysts, and the influence from synergy effects between dopants, which paves the way for the rational design of novel metal-free catalysts for CO2 electro-reduction.

The silicon on glasses process is a common preparation method of micro-electro-mechanical system inertial devices, which can realize the processing of thick silicon structures. This paper proposes that indium tin oxides (ITO) film can serve as a deep silicon etching cut-off layer because ITO is less damaged under the attack of fluoride ions. ITO has good electrical conductivity and can absorb fluoride ions for silicon etching and reduce the reflection of fluoride ions, thus reducing the foot effect. The removal and release of ITO use an acidic solution, which does not damage the silicon structure. Therefore, the selection of the sacrificial layer has an excellent effect in maintaining the shape of the MEMS structure. This method is used in the preparation of MEMS accelerometers with a structure thickness of 100 μm and a feature size of 4 μm. The over-etching of the bottom of the silicon structure caused by the foot effect is negligible. The difference between the simulated value and the designed value of the device characteristic frequency is less than 5%. This indicates that ITO is an excellent deep silicon etch stopper material.

As metal-free catalysts with great potential for widespread application, nanostructured carbon materials have excellent performance comparable to traditional metal oxide catalysts in the oxidative ...

Li–S batteries have aroused intense interests as one of the most promising high-energy-density storage technology. However, the complex undesired shuttle effect induced by dissolution and diffusion of lithium polysulfide intermediates remains the major setback of this technology. Chemical modification of carbon cathode through heteroatom-doping is widely accepted as an effective method to inhibit the shuttle effect in Li-S battery cathode. Herein, using first principle calculations, we systematically examined the interaction between halogenated graphene and lithium polysulfide species. It is found that the halogen dopants (F, Cl, Br, I) significantly modify the local electronic structure of adsorption site and further induce a polarization to trap the polysulfides. Interestingly, a concave curve is observed from F to I for lithium polysulfide adsorption rather than a linear relation. The exceptions demonstrated from iodine dopant is carefully analyzed and attributed to its unique charge state. Moreover, boron as second dopant further strengthens the interaction between halogenated graphene and polysulfide molecule. Based on halogenation strategy, lithium polysulfide/cathode interactions are tuned in a wide range, which can also be of great importance to accelerate redox reaction in Li-S battery. Overall, an effective method by halogenation is verified to regulate the adsorption of lithium polysulfide and also enhance the reaction kinetics of the Li-S battery system.

Dry reforming of methane (DRM) is one of the effective catalytic routes to utilize methane and carbon dioxide molecules. The supported Ni catalysts on lanthanide oxides show remarkable reactivities...

Graphene quantum dots (GQDs) have been suggested to have a wide range of applications due to their unique electronic and optical properties. Moreover, heteroatom doping has become a viable way to fine-tune the properties of GQDs. However, the working principle of the doping strategy is still not conclusive. In this study, the effects of size, configuration of the nitrogen dopant, and N/C ratio on the electronic and optical properties of GQDs have been carefully examined. First, the variation of the adsorption wavelength of pristine GQDs was evaluated for which a linear relation is established against different diameters. Moreover, it is found that both the configuration and content of nitrogen dopants have a significant impact on the adsorption wavelength and band gap of GQDs. In particular, different nitrogen species could have exactly opposite effects on the adsorption behavior. The origin of the nitrogen doping effect is calibrated from orbital localization, charge analysis, natural transition orbitals, and atomic contribution towards excitation. It is noted that nitrogen doping can simultaneously reduce both light adsorption energy and emission energy compared with the pristine one. This study provides an insightful explanation for the electronic and optical properties of GQDs and consolidates the theory base of the doping strategy.

In this paper, we propose a novel method for pedestrian dead reckoning (PDR) using microelectromechanical system magnetic, angular rate, and gravity sensors, which includes a double-step unscented Kalman filter (DUKF) and hidden Markov model (HMM)-based zero-velocity-update (ZVU) algorithm. The DUKF divides the measurement updates of the gravity vector and the magnetic field vector into two steps in order to avoid the unwanted correction for the Euler angle error. The HMM-based ZVU algorithm is developed to recognize the ZVU efficiently. Thus, the proposed PDR method can reduce the position drift caused by the heading error and fault zero-velocity measurement. Experimental results demonstrate that the proposed method achieves better yaw estimate, as well as zero-velocity measurement, and obtains more accurate dead-reckoning position than other methods in the literature.

In this work, for the first time it is demonstrated that supported single Au in either a positive or a negative charge state can catalyze acetylene hydrochlorination competitively with regard to ot...

In this paper, we report a novel aluminum nitride (AlN) resonant micro-electromechanical systems (MEMS) accelerometer. The spring beams are T-shaped with two masses hanged at the end. This accelerometer is sensitive to the $z$ -axis acceleration due to a thin thickness. Different from the working mechanism of the ordinary MEMS resonant accelerometers, masses of this accelerometer are excited to resonate in-plane. In addition the stiffness of spring beams changes significantly when an out plane ( $z$ -axis) inertial force applied on the structure. Therefore, the resonant frequency of the structure will change with the out-plane inertial force. The resonant properties and sensitivities of this AlN accelerometer are simulated by COMSOL Multiphysics. The accelerometer is fabricated and tested. The size of the whole structure is $464\times 650\,\,\mu \text{m}^{2}$ . The resonant frequency is 16.10925 kHz at the static state. The sensing-axis sensitivity of this accelerometer is 1.11 Hz/g (i.e., 68.9 ppm/g) tested from −5g to +5g. The linearity of the accelerometer is 0.9954. The cross-axis sensitivities are 0.053 Hz/g ( $x$ -axis) and 0.048 Hz/g ( $y$ -axis) respectively. The temperature coefficient of frequency (TCF) of this accelerometer is 0.815 Hz/ °C (i.e., 50.6 ppm/°C), tested from 0 °C to 50 °C. [2019-0062]

Halogenation is one of the most important ways to tailor the properties of graphene. We demonstrate for the first time that boron and nitrogen doping can effectively tune the interactions between halogen diatomic molecules and graphene from first principles calculations. Boron and nitrogen doping disrupt the regular pi-electron pattern and create spin density and orbital polarization. More interesting, nitrogen and boron doping not only significantly increases the binding energies of Cl2, Br2, and I2 but also induces the spontaneous dissociation of F2. The tunable effects from nitrogen and boron doping can adjust the interactions in a wide range. Overall, it is suggested that doping can be a very promising method for the facile halogenation of graphene.

With the development of the designing and manufacturing level for micro-electromechanical system (MEMS) gyroscopes, the control circuit system has become a key point to determine their internal performance. Nevertheless, the phase delay of electronic components may result in some serious hazards. This study described a real-time circuit phase delay correction system for MEMS vibratory gyroscopes. A detailed theoretical analysis was provided to clarify the influence of circuit phase delay on the in-phase and quadrature (IQ) coupling characteristics and the zero-rate output (ZRO) utilizing a force-to-rebalance (FTR) closed-loop detection and quadrature correction system. By deducing the relationship between the amplitude-frequency, the phase-frequency of the MEMS gyroscope, and the phase relationship of the whole control loop, a real-time correction system was proposed to automatically adjust the phase reference value of the phase-locked loop (PLL) and thus compensate for the real-time circuit phase delay. The experimental results showed that the correction system can accurately measure and compensate the circuit phase delay in real time. Furthermore, the unwanted IQ coupling can be eliminated and the ZRO was decreased by 755% to 0.095°/s. This correction system realized a small angle random walk of 0.978°/√h and a low bias instability of 9.458°/h together with a scale factor nonlinearity of 255 ppm at room temperature. The thermal drift of the ZRO was reduced to 0.0034°/s/°C at a temperature range from −20 to 70 °C.

In this paper, we report a novel teeter-totter type accelerometer based on glass-silicon composite wafers. Unlike the ordinary micro-electro-mechanical systems (MEMS) accelerometers, the entire structure of the accelerometer, includes the mass, the springs, and the composite wafer. The composite wafer is expected to serve as the electrical feedthrough and the fixed capacitance plate at the same time, to simplify the fabrication process, and to save on chip area. It is manufactured by filling melted borosilicate glass into an etched silicon wafer and polishing the wafer flat. A sensitivity of 51.622 mV/g in the range of &plusmn, 5 g (g = 9.8 m/s2), a zero-bias stability under 0.2 mg, and the noise floor with 11.28 &micro, g/&radic, Hz were obtained, which meet the needs of most acceleration detecting applications. The micromachining solution is beneficial for vertical interconnection and miniaturization of MEMS devices.

Graphene quantum dots (GQDs) have been suggested to have a wide range of applications due to their unique electronic and optical properties. Moreover, heteroatom doping has become a viable way to fine-tune the properties of GQDs. However, the working principle of the doping strategy is still not conclusive. In this study, the effects of size, configuration of the nitrogen dopant, and N/C ratio on the electronic and optical properties of GQDs have been carefully examined. First, the variation of the adsorption wavelength of pristine GQDs was evaluated for which a linear relation is established against different diameters. Moreover, it is found that both the configuration and content of nitrogen dopants have a significant impact on the adsorption wavelength and band gap of GQDs. In particular, different nitrogen species could have exactly opposite effects on the adsorption behavior. The origin of the nitrogen doping effect is calibrated from orbital localization, charge analysis, natural transition orbitals, and atomic contribution towards excitation. It is noted that nitrogen doping can simultaneously reduce both light adsorption energy and emission energy compared with the pristine one. This study provides an insightful explanation for the electronic and optical properties of GQDs and consolidates the theory base of the doping strategy.

With the miniaturization of micro-electro-mechanical system (MEMS) gyroscopes, it is necessary to study their nonlinearity. The phase-frequency characteristics, which affect the start-up time, are crucial for guaranteeing the gyroscopes&rsquo, applicability. Nevertheless, although the amplitude-frequency (A-f) effect, one of the most obvious problems in nonlinearity, has been well studied, the phase response of nonlinear gyroscopes is rarely mentioned. In this work, an elaborate study on the characteristics and locking process of nonlinear MEMS gyroscopes is reported. We solved the dynamic equation using the harmonic balance method and simulated the phase-locked loop (PLL) actuation process with an iterative calculation method. It was shown that there existed an apparent overhanging and multi-valued phenomenon in both the amplitude&ndash, frequency and phase&ndash, frequency curves of nonlinear gyroscopes. Meanwhile, it was ascertained by our simulations that the locking time of PLL was retarded by the nonlinearity under certain conditions. Moreover, experiments demonstrating the effect of nonlinearity were aggravated by the high quality factor of the drive mode due to the instability of the vibration amplitude. A nonlinear PLL (NPLL) containing an integrator was designed to accelerate the locking process. The results show that the start-up time was reduced by an order of magnitude when the appropriate integral coefficient was used.

As the commercial catalyst in the propane direct dehydrogenation (PDH) reaction, one of the biggest challenges of Pt catalysts is coke formation, which severely reduces activity and stability. In this work, a first-principles DFT-based kinetic Monte Carlo simulation (kMC) is performed to understand the origin of coke formation, and an effective method is proposed to curb coke. The conventional DFT calculations give a complete description of the reaction pathway of dehydrogenation to propylene, deep dehydrogenation, and C–C bond cracking. The rate-limiting step is identified as the dissociative adsorption of propane. Moreover, a comparison between different exchange-correlation functionals indicates the importance of van der Waals corrections for the adsorption of propane and propylene. The lateral interactions between the surface adsorbates are significant, which implies that mean field microkinetic modeling might not adequately describe the reaction process. There are two distinct stages in PDH, which ar...

Doping with heteroatoms, such as nitrogen and boron, is crucial for the good performance of metal-free carbon cathode catalysts in the CO2 electrochemical reduction reaction (CERR). In this report, for the first time phosphorus is used to fabricate carbon catalysts and it is found that the bonding configuration of phosphorus has a key effect on the performance of the CERR. Two different phosphorus doped onion-like carbon (P-OLC) catalysts are synthesized with P–O bonding or P–C bonding as the major phosphorus bonding configuration, respectively. Compared to P-OLC with P–O bonding, P-OLC with P–C bonding exhibits a much better CERR performance, with a partial current density of 4.9 mA cm−2, 81% faradaic efficiency, and excellent durability (27 h) at low potential (−0.90 V vs. SHE). Density functional theory calculations show that the binding energy of the key intermediate COOH* in P–C bonding is much higher than that of its counterpart in P–O bonding, which is beneficial for lowering the energy barrier of the rate-limiting step. The better reactivity of the P–C bonding site is also verified by aromaticity analysis. Moreover, ultraviolet photoelectron spectroscopy (UPS) and partial density of state (PDOS) analysis suggest that the electron transfer capability of P–C bonding is stronger than that of P–O bonding. The current study demonstrates that phosphorus doping is an effective strategy for fabricating carbon CERR catalysts and reveals the pivotal role of the phosphorus bonding configuration.

As emerging as highly active metal-free acetylene hydrochlorination catalyst, recently boron nitride attracted great attentions from both experimental and computational explorations. In this work, the carbon doping is verified to be indispensable to trigger the activities of pristine h-BN catalyst from first principles calculations. The effects on electronic structure of h-BN induced by carbon doping are examined from ELF, PDOS, and charge analysis which have direct impacts on the catalytic capabilities. The pathways can be categorized to be either C2H2 or HCl adsorption as first step. Although these two categories have distinct limiting step and mechanism, the shared feature is that the activation of C2H2 is key to the vinyl chloride formation. Furthermore, TOFs of different pathways are calculated to determine the most favorable catalytic route and is in a qualitatively agreement with largest barrier of elementary step. The importance of HCl-starting pathway is revealed from the comparison of TOF which is severely underestimated previously. In the end, the deep reactions which might be leading to precursor of cokes are explored and shed lights on the origin of superior stability of catalyst.

In this paper, we report a novel aluminum nitride (AlN) thin-film piezoelectric resonant accelerometer. Different from the ordinary MEMS (micro-electro-mechanical systems) resonant accelerometers, the entire structure of the accelerometer, including the mass and the springs, is excited to resonate in-plane, and the resonance frequency is sensitive to the out-plane acceleration. The structure is centrosymmetrical with serpentine electrodes laid on supporting beams for driving and sensing. The stiffness of the supporting beams changes when an out-plane inertial force is applied on the structure. Therefore, the resonance frequency of the accelerometer will also change under the inertial force. The working principle is analyzed and the properties are simulated in the paper. The proposed AlN accelerometer is fabricated by the MEMS technology, and the structure is released by an ICP isotropic etching. The resonance frequency is 24.66 kHz at a static state. The quality factor is 1868. The relative sensitivity of this accelerometer, defined as the shift in the resonance frequency per gravity unit (1 g = 9.8 m/s2) is 346 ppm/g. The linearity of the accelerometer is 0.9988. The temperature coefficient of frequency (TCF) of this accelerometer is &minus, 2.628 Hz/&deg, C (i.e., &minus, 106 ppm/&deg, C), tested from &minus, 40 &deg, C to 85 &deg, C.

This paper reports the resonant properties of aluminum nitride (AlN) thin-film MEMS (micro-electromechanical systems) device. A T-shape structure is designed as a key sensitive component. Based on the piezoelectric effect of AIN, the whole structure can be excited to vibrate in-plane by top/bottom electrodes. In this work, a pair of paralleled top electrodes are used to excite the whole structure to vibrate in-plane (x-axis). A serpentine electrode can excite the whole structure to vibrate in-plane along the orthogonal direction (y-axis). The resonant properties were characterized by the dynamic signal analyzer. Resonant frequencies of the two modes are 25.1124 kHz and 24.5401 kHz. Quality factors of the two modes are 2130 and 2210, respectively. The effective efficiency of electromechanical transduction is 0.7848%. The resonant modes can be applied in MEMS gyroscopes or resonant accelerometers.

A novel three-dimensional (3D) hermetic packaging technique suitable for capacitive microelectromechanical systems (MEMS) sensors is studied. The composite substrate with through silicon via (TSV) is used as the encapsulation cap fabricated by a glass-in-silicon (GIS) reflow process. In particular, the low-resistivity silicon pillars embedded in the glass cap are designed to serve as the electrical feedthrough and the fixed capacitance plate at the same time to simplify the fabrication process and improve the reliability. The fabrication process and the properties of the encapsulation cap were studied systematically. The resistance of the silicon vertical feedthrough was measured to be as low as 263.5 m&Omega, indicating a good electrical interconnection property. Furthermore, the surface root-mean-square (RMS) roughnesses of glass and silicon were measured to be 1.12 nm and 0.814 nm, respectively, which were small enough for the final wafer bonding process. Anodic bonding between the encapsulation cap and the silicon wafer with sensing structures was conducted in a vacuum to complete the hermetic encapsulation. The proposed packaging scheme was successfully applied to a capacitive gyroscope. The quality factor of the packaged gyroscope achieved above 220,000, which was at least one order of magnitude larger than that of the unpackaged. The validity of the proposed packaging scheme could be verified. Furthermore, the packaging failure was less than 1%, which demonstrated the feasibility and reliability of the technique for high-performance MEMS vacuum packaging.