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Fe, Cu dual metal single atom catalyst on commercial carbon black exhibited excellent oxygen reduction reaction performance.

Background Therapeutic monoclonal antibodies targeting complement C5 have proven to be a very effective approach for the treatment of complement-associated diseases including paroxysmal nocturnal hemoglobinuria (PNH). However, C5 antibody alone often cannot sufficiently block the alternative pathway (AP) of the complement system, nor reduce the deposition of C3b on the cell surface produced by C3 activation, and even increase the deposition, which is considered to be the cause of extravascular hemolysis in PNH patients treated with C5 antibody. As a natural and powerful complement inhibitor, CR1 has potential for drug development, but shows poor druggability due to low yield, short PK etc. Here, by fusing different CR1 fragments with the C5 antibody, we tried to obtain a fusion protein with good yield, purity and activity. Methods Candidate fusion proteins were generated by transient transfection expression and purified via Protein A affinity chromatography. Their bioactivities were investigated by in vitro classical pathway (CP)- and AP-mediated hemolysis assays. C3b deposition was calculated by flow cytometry. The PK/PD characteristics of optimized fusion proteins were tested in wildtype and human C5 transgenic mice, as well as cynomolgus monkeys. The therapeutic effect of the final product for complement-associated diseases was examined in collage antibody induced arthritis (CAIA) model mice. Results By fusing the mutated short consensus repeat (SCR) 1–5 fragment of CR1 to N-terminal of the heavy chain of C5 antibody, modifying surface charge and attaching linkers, we finally obtained a bifunctional complement inhibitory fusion protein with higher yield and superior CP and AP inhibitory activities. It showed a capability to inhibit C3 fragment deposition and therapeutic potential for CAIA, with one-week in vivo sustained bioactivity. Conclusions The fusion protein has the potential to become a more comprehensive complement activity-inhibiting drug, which may overcome the inefficiency of C5 antibody therapy.

A one-pot, two-step aza-Michael/Michael/Michael process was developed to diastereospecifically construct C6a,C10a

Quantum dots (QDs) have recently attracted intensive attention for electrode materials due to their tunable physical dimensions, unique surface effect and pseudocapacitive property. Nevertheless, direct employment of QDs as electrode materials are plagued because of their intrinsic aggregation. In this work, we have successfully fabricated amorphous FeOOH QDs and FeOOH/g-C3N4 hybrid nanosheets as electrode materials using a scalable and bottom-up synthesis route. The FeOOH/g-C3N4 composite possesses a unique heterostructure, comprising a highly dispersed FeOOH QDs anchored on g-C3N4 nanosheets. We probe the behavior of as-prepared hybrid sample, which collectively delivers significant improvement in terms of ultrahigh specific capacitance and long-term stability. The FeOOH/g-C3N4-20 electrode exhibits a large specific capacitance of about 270.8 F g−1 at 1 A g −1, prominent rate capability at high scan rates, and favorable capacitance retention (78.3% capacitance retention after 3000 cycles).

Electrochemical conversion of CO2 to useful products at temperatures below 100 °C is nearing the commercial scale. Pilot units for CO2 conversion to CO are already being tested. Units to convert CO2 to formic acid are projected to reach pilot scale in the next year. Further, several investigators are starting to observe industrially relevant rates of the electrochemical conversion of CO2 to ethanol and ethylene, with the hydrogen needed coming from water. In each case, Faradaic efficiencies of 80% or more and current densities above 200 mA cm−2 can be reproducibly achieved. Here we describe the key advances in nanocatalysts that lead to the impressive performance, indicate where additional work is needed and provide benchmarks that others can use to compare their results. This Perspective describes the key advances in nanocatalysts that have led to the impressive electrochemical conversion of CO2 to useful products and provides benchmarks that others can use to compare their results.

Developing efficient and stable Pt-based oxygen reduction reaction (ORR) catalysts is a way to promote the large-scale application of fuel cells. Pt-based alloy nanowires are promising ORR catalysts, but their application is hampered by activity loss caused by structural destruction during long-term cycling. Herein, the preparation of ordered PtFeIr intermetallic nanowire catalysts with an average diameter of 2.6 nm and face-centered tetragonal structure (fct-PtFeIr/C) is reported. A silica-protected strategy prevents the deformation of PtFeIr nanowires during the phase transition at high temperature. The as-prepared fct-PtFeIr/C exhibited superior mass activity for ORR (2.03 A mg

The electrochemical hydrogen evolution is a key technology for future renewable energy conversion and storage. Platinum is the most efficient catalyst for hydrogen evolution reaction (HER), but its mass activity should be boosted further. Herein, we deposited platinum on nitrogen-doped vertical graphene through an atomic layer deposition method. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy confirmed that the platinum was highly dispersed on the array substrate. On account of the array structure and high dispersion of platinum, the synthesized catalyst exhibited high HER performance with a low overpotential of 42 mV at 10 mA cm−2 and a low Tafel slope of 52.2 mV dec−1. Significantly, the synthesized catalyst exhibited a high mass activity of 4.45 A mg−1 Pt, which was ∼13 times higher than that of commercial Pt/C.

There is a growing demand for high precision positioning and navigation technologies for land vehicles, especially with the fast-emerging autonomous operation. Developing a robust vehicle navigation system that works well in all environments is still a challenging problem for automated level 2 driving. Global Navigation Satellite System (GNSS) receivers, Inertial Measurement Units (IMUs), and wheel odometers have been widely used to tackle this problem. GNSS Precise Point Positioning (PPP) has become an attractive high precision alternative that can provide sub-meter level accuracy in favorable environments with no need for reference stations. Yet, such an accuracy degrades in challenging environments where the GNSS signals are attenuated or completely blocked. To reach robust and continuous navigation performance, PPP can be integrated with other navigation systems such as the Inertial Navigation System (INS). This paper demonstrates the performance of Profound-IP3/DR, a low-cost PPP/INS integrated navigation system, recently developed by Profound Positioning Inc (PPI). The system is primarily targeting high precision vehicular navigation that requires continuous sub-meter level positioning accuracy along highways, even while driving along bridges and overpasses. Profound-IP3/DR also provides robust and competitive performance in suburban and urban environments. The integration with inertial sensors relies on Micro-Electro-Mechanical System (MEMS) grade IMU to maintain the system’s low-cost for wide adoption. Profound Positioning Inc. distributes the integrated navigation module to its customers as a software library or a turnkey system to be easily integrated for various automated driving applications. Profound-IP3/DR was tested and validated through various road tests that cover good line-of-sight (LOS) GNSS environments, suburban, short GNSS outages, and complete GNSS outages. The test results indicate that the system can maintain sub-meter positioning accuracy in open-sky and suburban areas. For complete GNSS outage scenarios (e.g., an underground parking lot) and downtown scenarios with severe multipath, it shows robust long-term performance with meter-level accuracy. Based on the results, Profound-IP3/DR is expected to benefit low-cost, continuous, and precise land vehicular navigation and is ready for utilization in automated level 2 driving applications. The test results indicate that • In the open-sky environment, benefiting from the favorable GNSS LOS conditions, the Profound-IP3/DR solution mostly follows the IP3 solution with sub-meter level accuracy. • During highway driving with several overhead bridges crossed, the Profound-IP3/DR solution smooths the spikes/jumps from the IP3 solutions due to the limited visible number of satellites and cycle slips when driving under the overpasses. Moreover, the proposed IP3/DR could bridge the transitory GNSS blockages by keeping sub-meter level accuracy and maintains continuous performance. • For a typical downtown environment, Profound-IP3/DR outperforms the standalone IP3 solution and improves its degraded performance due to the challenges of severe multipath, poor satellite geometry, and signal blockage, etc. The system recognizes the GNSS environment and automatically weights the GNSS updates accurately. The smart combination of GNSS updates and inertial sensor measurements result in continuous meter-lever accuracy in such challenging environments. • In a typical underground parking scenario, when GNSS is not available, and there is no PPP solution, Profound-IP3/DR could continuously provide a reliable navigation solution with meter-level accuracy. Profound-IP3/DR has the advantage of providing a reliable and continuous positioning solution in all environments while utilizing low-end consumer-level inertial sensors and GNSS receivers. The high positioning accuracy opens the door for Profound-IP3/DR to be a key player in continuous and precise vehicular navigation applications such as asset tracking and safety assurance. The continuous sub-meter level positioning accuracy along highways makes Profound-IP3/DR ideal for automated level 2 driving applications.

With strong demands on precise positioning for mass-market applications from self-driving cars, UAV and smartphones, PPP systems and products based on low-cost GNSS chipsets and modules targeted for consumer markets are being developed and released to the markets. To date, most systems and products are operated in open-sky environments while only few were tested in sub-urban environments. It is time to investigate and develop low-cost PPP system and products for precise positioning in urban environments. Although with various challenges, this presentation will describe a low-cost single-frequency PPP system that has been successfully demonstrate 50 cm accuracy in open-sky and sub-urban environments and further enhanced to support precise positioning in urban environments. Featuring multi-constellations, global availability, fast convergence and continuous navigation solutions, Instant PPP (IP3) is developed as an ideal precise positioning solution for mass market applications. The availability and accuracy of IP3 in urban environments such as downtown area will be discussed and presented. In order to obtain high-accuracy and high-availability positioning solutions in urban environments, the IP3 library is uniquely designed and enhanced in several aspects. For instance, the instant receiver velocity based on the Doppler observations and the coordinate changes calculated from the carrier phase differences between two consecutive epochs are integrated for the one-step prediction of the receiver positions in the Kalman filter. Meanwhile, the weight of carrier phase, pseudo-range and Doppler observations are smartly tuned as a function of Signal to Noise Ratio (SNR) respectively. Additionally, the quality control part is designed to be adaptive to different scenarios, such as open-sky or urban environments. The receiver clock drifts for different constellations are specifically modelled in the velocity estimation to increase the degrees of freedom, which further enhances the solution availability in the extreme challenging situations. To evaluate the availability and accuracy of IP3 library in urban environments, several real-time vehicle-based field tests have been carried out with the IP3 evaluation kit in Calgary, Canada. The IP3 evaluation kit consists of a u-blox M8T module, an ARM based processor and a patch antenna. The raw GNSS data from GPS, GLOANSS and Galileo were logged and processed in real-time, with the real-time corrections streaming over Wi-Fi, which is connected to the cellphone hotspot. A navigation-grade IMU (KVH1750) and a high-end NovAtel Propak6 GNSS receiver were used as the reference system in the tests. Meanwhile, the 1 Hz GNSS raw observations from a nearby base station (UCAL) was streamed and stored for the generation of the accurate RTK/INS reference solutions, which were processed in post-mission by commercial software. The testing results indicate the IP3 library can provide 50 cm accuracy in the sub-urban areas with 100% solution availability. When comes to the urban environment such as downtown area with abundant high buildings, the positioning Root-Mean-Square error (RMS) of IP3 degrades to meter level while the solution availability remains 100%. In the typical urban environments, the GNSS observations are all affected at different levels. For example, the availability of pseudo-range and Doppler observations are much higher than the carrier phase observations in challenging urban areas, nevertheless they are more vulnerable to the multipath effects. According to the tests, the SNR can largely reflect the change of the environments and thus was used in the weighting process for different types of observations. Apart from the positioning results, the accuracy and availability of the velocity solution are also evaluated in the urban environments. The RMS of IP3 velocity solution in the sub-urban area is at centimeter level while degrades to decimeter level in urban area such as downtown. Additionally, the standard deviations of the positioning and velocity solutions outputted by IP3 library match well with the true errors, hence the IP3 library can be conveniently and easily integrated with other navigation systems such as inertial navigation system (INS). More field tests will be carried out in different urban areas and the results will be presented lately. IP3 can provide precise positioning solutions with low-cost GNSS receivers even in urban environments. By novel integration of low-cost GNSS and PPP technology, IP3 is an ideal precise positioning solution for mass-market applications and can be easily integrated with other navigation systems such INS.

Electrochemical conversion of CO

As an advanced and efficient high-precision positioning technology, Precise Point Positioning (PPP) is capable of providing precise navigation solutions globally with the Global Navigation Satellite System (GNSS) observations from a single receiver. Benefiting from maturation of the communication infrastructure, the precise products such as satellite orbit and satellite clock corrections are currently widely available with low latency, which opens doors for its applications to various emerging applications, such as self-driving cars. The rapid rise of the low-cost GNSS receivers and chipsets is pushing on the development of low-cost and robust navigation systems with strong industry demands. To meet this market demand, the Instant PPP (IP3) featuring multi-constellations, global availability, fast convergence and continuous navigation solutions (even with GNSS correction outages) is developed. IP3 can provide navigation solution with half meter (50 cm) (Circular Error Probability (CEP) 50%) accuracy in real-time with orbits, clocks and ionosphere and code bias corrections and using observations from a single frequency (SF) GNSS receiver. To mitigate the effects of GNSS signal blockages and multipath in challenging environments, IP3/DR integration is proposed in this research by combining the IP3 with low-cost inertial navigation system (INS) to provide continuous and robust navigation solutions. We will first introduce the scheme of IP3/DR system as well as the key features. Afterwards, the performance of the IP3/DR system will be verified in three different situations, namely the normal situation with open-sky and sub-urban environment, the field test with GNSS corrections outage and the field test with GNSS observations outage. The results of the above three experiments indicate the IP3/DR can provide high precision navigation solution better than 50 cm (CEP 50%) even with 5 minutes GNSS corrections outage and short-term GNSS observations outage.

An enantioselective (92-99% ee) Michael/aldol cascade reaction between 4,4,4-trifluoroacetoacetates and α,β-unsaturated enones was established in the presence of cinchona alkaloid-based primary amines. Various β-CF3-cyclohexanones were constructed in high yields (81-99%) as a couple of separable diastereomers. This tandem reaction was sensitive to acidic co-catalysts, with a Michael/aldol condensation process favorably occurring to generate β-CF3-cyclohexenones (42-69% yield, 84-96% ee) in the presence of trifluoroacetic acid.

With increased measurement quality of low-cost Global Navigation Satellite System (GNSS) receivers, Precise Point Positioning (PPP) becomes feasible using a low-cost multi-constellation single-frequency GNSS receiver. Profound Instant PPP (IP3), for example, is a real-time fast convergence PPP technology that offers world-wide 50-cm circular error probability (CEP) PPP solution using a low-cost GNSS chipset. IP3 is able to output precise positioning solutions within seconds, which makes it suitable for various emerging applications such as self-driving cars, UAV and smartphones. With strong demand on higher accuracy by those applications, several low-cost dual-frequency GNSS chipset products (e.g. u-blox F9P, Broadcom BCM47755, etc.) have been released to market. The availability of GNSS observations at the second frequency can further improve the positioning accuracy with low-cost GNSS chipsets. Compared to single-frequency PPP, a dual-frequency PPP system not only increases the redundancy of the positioning system but also helps mitigate the ionospheric effect, leading to more accurate and robust positioning solutions. This paper describes the development of a dual-frequency based Instant PPP system (DF-IP3) using low-cost multi-constellation dual-frequency GNSS chipsets. This system is able to output precise positioning solutions at 30 cm CEP within a few seconds and can be applied to support a wide range of applications.

Precise Point Positioning (PPP) has become an attractive topic as consumer low-cost receivers are able to provide raw observations and signals with multiple frequencies and support multiple GNSS systems. Generally, PPP can provide sub-meter level accuracy in favorable environments. However, such an accuracy degrades in challenging environments where the GNSS observations are attenuated or blocked. In order to reach seamless and reliable navigation performance, in this research, PPP is designed to integrate with a low-cost IMU which runs the Inertial Navigation System (INS) algorithm on it. A low-cost Profound-IP3/DR (dead reckoning) integrated navigation system targeted for precise vehicular navigation is proposed. The integrated system is accessed through various road tests which cover good LOS GNSS environments, sub-urbans, short-term GNSS outages, and complete GNSS outages. The results indicate that the Profound-IP3/DR is able to maintain sub-meter RMS accuracy in open-sky and sub-urban areas. For complete GNSS outages and challenging downtown environments with severe multi-path and signal blockages, the Profound-IP3/DR shows robust long-term performance with decimeter to meter-level accuracy. The high positioning accuracy supports Profound-IP3/DR to be a key player in continuous and precise vehicular navigation applications such as asset tracking and car navigation. Moreover, such accurate navigation performance shows the potential and readiness to be integrated with other sources of update such as vision, LiDAR, radar and digital maps to fully benefit the technologies for navigation of autonomous systems.

To meet the increasing demands from the real-time Precise Point Positioning (PPP) users, the real-time satellite orbit and clock products are generated by different International GNSS Service (IGS) real-time analysis centers and can be publicly received through the Internet. Based on different data sources and processing strategies, the real-time products from different analysis centers therefore differ in availability and accuracy. The main objective of this paper is to evaluate availability and accuracy of different real-time products and their effects on real-time PPP. A total of nine commonly used Real-Time Service (RTS) products, namely IGS01, IGS03, CLK01, CLK15, CLK22, CLK52, CLK70, CLK81 and CLK90, will be evaluated in this paper. Because not all RTS products support multi-GNSS, only GPS products are analyzed in this paper. Firstly, the availability of all RTS products is analyzed in two levels. The first level is the epoch availability, indicating whether there is outage for that epoch. The second level is the satellite availability, which defines the available satellite number for each epoch. Then the accuracy of different RTS products is investigated on nominal accuracy and the accuracy degradation over time. Results show that Root-Mean-Square Error (RMSE) of satellite orbit ranges from 3.8 cm to 7.5 cm for different RTS products. While the mean Standard Deviations of Errors (STDE) of satellite clocks range from 1.9 cm to 5.6 cm. The modified Signal In Space Range Error (SISRE) for all products are from 1.3 cm to 5.5 cm for different RTS products. The accuracy degradation of the orbit has the linear trend for all RTS products and the satellite clock degradation depends on the satellite clock types. The Rb clocks on board of GPS IIF satellites have the smallest degradation rate of less than 3 cm over 10 min while the Cs clocks on board of GPS IIF have the largest degradation rate of more than 10 cm over 10 min. Finally, the real-time kinematic PPP is carried out to investigate the effects of different real-time products. The CLK90 has the best performance and mean RMSE of 26 globally distributed IGS stations in three components are 3.2 cm, 6.6 cm and 8.5 cm. And the second-best positioning results are using IGS03 products.

Water electrolyzers are being developed as a way of storing renewable energy, as a way to produce hydrogen for fuel cell automobiles, and as a route to renewable fuels and chemicals. In this paper the performance of an alkaline water electrolyzers at 60 °C with 1 M KOH and iron/nickel/cobalt catalysts with several different membranes: Sustainion® 37–50, Fumasep FAS-50, Fumasep FAPQ, Neosepta ACM, AMI 7001, Nafion® 115, and Celazole® PBI. Measured area specific resistances (ASR) at 60 °C with 1 M KOH varied from 0.045 Ω-cm2 with Sustainion® 37–60 to over 50 Ω-cm2 with Neosepta ACM. The current at a cell potential of 1.9 V varied from 1 A/cm2 with Sustainion® 37, 0.5 A/cm2 with Fumasep FAS-50, 0.17 A/cm2 with Fumasep FAPQ and less than 0.1 A/cm2 for Neosepta ACM, AMI 7001, Nafion 115 and Celazole® PBI. Constant current runs at 1 A/cm2 were done with the Sustainion® 37 membranes and the Fumasep FAS-50. The cell with the Sustainion® 37 membrane was very stable. The voltage to maintain 1 A/cm2 rose only 3–5 μV/h over a 2000 hr run. In contrast, the voltage to maintain 1 A/cm2 in the cell with the FAS-50 membrane showed over 200 μV/h increase and failed after 200 h. One Sentence Summary: The paper shows that one can double the current output of an alkaline water electrolyzer by using Sustainion® 37 membranes.

The GPS satellite clock offset prediction is investigated and applied to a real-time PPP system. First, the current situation of GPS satellite clock is introduced and analysed with respect to their...

Formic acid generated from CO2 has been proposed both as a key intermediate renewable chemical feedstock as well as a potential energy storage chemical media for hydrogen. In this paper, we describe a novel three compartment electrochemical cell configuration with the capability of directly producing a pure formic acid product in the concentration range of 5 – 20 wt% at high current densities and Faradaic yields. The electrochemical cell employs a Dioxide Materials Sustainion™ anion membrane, allowing for the improved CO2 electrochemical reduction performance. Stable electrochemical cell performance for more than 500 hours has been experimentally demonstrated.

Formic acid generated from CO2 has been proposed both as a key intermediate renewable chemical feedstock as well as a potential chemical-based energy storage media for hydrogen. In this paper, we describe a novel three-compartment electrochemical cell configuration with the capability of directly producing a pure formic acid product in the concentration range of 5–20 wt% at high current densities and Faradaic yields. The electrochemical cell employs a Dioxide Materials Sustainion™ anion exchange membrane and a nanoparticle Sn GDE cathode containing an imidazole ionomer, allowing for improved CO2 electrochemical reduction performance. Stable electrochemical cell performance for more than 500 h was experimentally demonstrated at a current density of 140 mA cm−2 at a cell voltage of only 3.5 V. Future work will include cell scale-up and increasing cell Faradaic performance using selected electrocatalysts and membranes.

Chemically controlling crystal structures in nanoscale is challenging, yet provides an effective way to improve catalytic performances. Pt-based nanoframes are a new class of nanomaterials that have great potential as high-performance catalysts. To date, these nanoframes are formed through acid etching in aqueous solutions, which demands long reaction time and often yields ill-defined surface structures. Herein we demonstrate a robust and unprecedented protocol for facile development of high-performance nanoframe catalysts using size and crystallographic facet-controlled PtNi4 tetrahexahedral nanocrystals prepared through a colloidal synthesis approach as precursors. This new protocol employs the Mond process to preferentially dealloy nickel component in the ⟨100⟩ direction through carbon monoxide etching of carbon-supported PtNi4 tetrahexahedral nanocrystals at an elevated temperature. The resultant Pt3Ni alloy tetrahexahedral nanoframes possess an open, stable, and high-indexed microstructure, containin...

CO2 electrolysis is a key step in CO2 conversion into fuels and chemicals as a way of mitigating climate change. We report the synthesis and testing of a series of new anion-conductive membranes (tradenamed Sustainion™) for use in CO2 electrolysis. These membranes incorporate the functional character of imidazolium-based ionic liquids as co-catalysts in CO2 reduction into a solid membrane with a styrene backbone. We find that the addition of an imidazolium group onto the styrene side-chains increases the selectivity of the reaction from approximately 25 % to approximately 95 %. The current at 3 V is increased by a factor of 14. So far we have been able to tune these parameters to achieve stable cells that provide current densities higher than 100 mA cm−2 at 3 V cell potential with a CO product selectivity over 98 %. Stable performance was observed for 6 months of continuous operation (>150 000 000 turnovers). These results demonstrate that imidazolium polymers are ideal membranes for CO2 electrolysis.

There is interest in metal single atom catalysts due to their remarkable activity and stability. However, the synthesis of metal single atom catalysts remains somewhat ad hoc, with no universal strategy yet reported that allows their generic synthesis. Herein, we report a universal synthetic strategy that allows the synthesis of transition metal single atom catalysts containing Cr, Mn, Fe, Co, Ni, Cu, Zn, Ru, Pt or combinations thereof. Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy and extended X-ray absorption fine structure spectroscopy confirm that the transition metal atoms are uniformly dispersed over a carbon black support. The introduced synthetic method allows the production of carbon-supported metal single atom catalysts in large quantities (>1 kg scale) with high metal loadings. A Ni single atom catalyst exhibits outstanding activity for electrochemical reduction of carbon dioxide to carbon monoxide, achieving a 98.9% Faradaic efficiency at −1.2 V., Single-atom catalysts are a promising class of catalytic materials, but general synthetic methods are limited. Here, the authors develop a ligand-mediated strategy that allows the large-scale synthesis of diverse transition metal single atom catalysts supported on carbon.

Real-time orbit and clock products are crucial for real-time precise point positioning (PPP) applications. The International Global Navigation Satellite System (GNSS) Service (IGS) launched the Real-Time Service (RTS) in 2013 to provide real-time satellite orbit and clock products which have since found wide applications. Currently, the IGS RTS provides two different types of satellite orbit and clock products: the products generated from individual Analysis Centers such as CLK01, CLK22 and CLK90 and the combination products such as IGS01 and IGS03. These IGS RTS products are different in terms of precision and reliability. First, we verify that the phenomenon of clock datum jumps is obvious in IGS01, which has not been considered by the GNSS community when applying the IGS01 product to the real-time PPP. Afterward, the causes of the clock datum jump are investigated. The results indicate that a switchover of the reference product or a datum jump in the reference product will cause a clock datum jump. In order to solve the clock datum jumps issue, a new clock datum jump detection and mitigation algorithm is proposed. Real-time kinematic PPP experiments are then carried out to validate the proposed satellite clock detection and mitigation algorithm. The positioning results with 27 globally distributed IGS stations show that the root mean square improvements in the north, east and up components are 61.5%, 36.5% and 55.1% after detecting and mitigating the datum jumps.

Precise satellite orbit and clock corrections are essential to precise point positioning (PPP). The standard GPS legacy navigation (LNAV) message disseminated by the satellite is one of the most widely used sources for deriving orbit and clock corrections in real-time using efficient analytical user algorithms. However, the quality of the satellite orbit and clock corrections computed with the standard LNAV is not adequate for real-time PPP mainly due to the low update rate. In this study, we proposed an improved LNAV which is estimated based on the IGS ultra-rapid (IGU) orbit and real-time service (RTS) clock products. Two advantages characterize this improved LNAV message. The first one is that scalable update rates can be used for disseminating satellite orbit and clock corrections. Users can decide to receive and decode the improved LNAV message at the desired update rate considering the availability of correction streams, communication bandwidth, and targeted accuracy. With sufficiently high update rates, the improved LNAV can be applied for high-precision applications such as real-time PPP. The second advantage is that the legacy user algorithms can be maintained for computing real-time satellite orbit and clock corrections. Since the improved LNAV has the same parameter representation as the standard LNAV, no changes are required at the user algorithms. To validate the proposed method, the quality of real-time orbit and clock corrections computed with the improved LNAV, IGU products, Centro Nacional de Estudios Espaciales (CNES) real-time products, and the standard LNAV is compared, while the IGS final products are used as the reference. The numerical results indicate that the improved LNAV can achieve comparable orbit accuracy as CNES real-time products, while the clock accuracy highly depends on the update rate. A globally distributed network of 40 IGS stations is used to assess the kinematic PPP performance. Using the improved LNAV with update intervals of 5 min, an average positioning accuracy of 0.122, 0.100, and 0.242 m at 95% confidence level can be obtained in the east, north, and up directions, respectively. Even when the update intervals extend to 2 h, the positioning accuracy is still about 1.2 times better than that of using IGU products. The proposed method provides a scalable and flexible way to improve the standard LNAV for real-time PPP users.

Fe single-atom catalysts (Fe SACs) with atomic FeNx active sites are very promising alternatives to platinum-based catalysts for the oxygen reduction reaction (ORR). The pyrolysis of metal-organic frameworks (MOFs) is a common approach for preparing Fe SACs, though most MOF-derived catalysts reported to date are microporous and thus suffer from poor mass transfer and a high proportion of catalytically inaccessible FeNx active sites. Herein, NH2 -MIL-101(Al), a MOF possessing a mesoporous cage architecture, is used as the precursor to prepare a series of N-doped carbon supports (denoted herein as NC-MIL101-T) with a well-defined mesoporous structure at different pyrolysis temperatures. The NC-MIL101-T supports are then impregnated with a Fe(II)-phenanthroline complex, and heated again to yield Fe SAC-MIL101-T catalysts rich in accessible FeNx single atom sites. The best performing Fe SAC-MIL101-1000 catalyst offers outstanding ORR activity in alkaline media, evidenced by an ORR half-wave potential of 0.94 V (vs RHE) in 0.1 m KOH, as well as excellent performance in both aqueous primary zinc-air batteries (a near maximum theoretical energy density of 984.2 Wh kgZn -1 ) and solid-state zinc-air batteries (a peak power density of 50.6 mW cm-2 and a specific capacity of 724.0 mAh kgZn -1 ).

The electrochemical reduction of CO2 to formate and formic acid has attracted a great amount of academic and commercial interest over the past five years. A number of experimental studies have generated data on the Faradaic performance and stability of various candidate catalyst materials in producing formate or formic acid. However, most of the data has been conducted at low current densities and over short time periods, typically hours to days. There is a critical need in providing long-term catalyst stability as well as electrolyzer-based operating data, which are needed for the commercial scale-up and operation of this technology, especially at high current densities. In this paper, the electrochemical CO2 conversion to pure formic acid was conducted using a three-compartment design electrolyzer, demonstrating electrolyzer catalyst and performance stability for over 1000 h at current densities up to 200 mA cm−2. Depending on the operation conditions, the electrolyzer directly produced a 6.03–12.92 wt% (1.3–2.8 M) formic acid product at Faradaic efficiencies ranging between 73.0–91.3%. Data on electrolyzer performance, including formic acid product generation rate, energy efficiency, and energy consumption are reported at three different current densities, 100, 200, and 250 mA cm−2. Lastly, a long term 1000 h electrolyzer stability run at 200 mA cm−2 is presented, providing information on the operating conditions required in obtaining stable electrolyzer performance. All the data will be extremely useful in the commercial scale-up of this technology.

The electrochemical production of syngas would enable production of chemicals and transportation fuels from carbon dioxide, water and renewable energy, but a suitable process at the moment does not exist. In this paper we consider two options for syngas production: (i) CO2 electrolysis to produce CO, water electrolysis to produce H2 and then mixing the CO and H2 to yield syngas; and (ii) the simultaneous co-electrolysis of CO2 and H2O in a single electrolyzer. The results show that both processes can produce syngas at industrially important rates. In this paper we demonstrate CO2 electrolysis at 100 mA/cm2, i.e., about 20 turnovers/s, and water electrolysis at 8 A/cm2 at 2.0 V/cell, with about 1,600 turnovers/s. Both systems are stable for a thousand hours or more, i.e., millions of turnovers. We also demonstrate simultaneous CO and H2 production in a single electrolyzer. These results demonstrate that syngas can be produced at industrially important rates via electrolysis.

This paper is a review on the application of imidazolium-based ionic liquids tethered to polymer backbones in the electrochemical conversion of CO2 to carbon monoxide and formic acid. These tethered ionic liquids have been incorporated into novel anion ion exchange membranes for CO2 electrolysis, as well as for ionomers that have been incorporated into the cathode catalyst layer, providing a co-catalyst for the reduction reaction. In using these tethered ionic liquids in the cathode catalyst composition, the cell operating current increased by a factor of two or more. The Faradaic efficiencies also increased by 20–30%. This paper provides a review of the literature, in addition to providing some new experimental results from Dioxide Materials, in the electrochemical conversion of CO2 to CO and formic acid.

Real-time single-frequency precise point positioning (RT-SF-PPP) has become a desired positioning approach because it can achieve high positioning accuracy with a low-cost global navigation satellite system (GNSS) chipset or receiver. For single-frequency precise point positioning (SF-PPP) applications, the ionospheric delay is a dominant error source, and thus the quality of applied ionospheric products is critical to the performance of SF-PPP. To meet the demands of the RT-SF-PPP users, the international GNSS service (IGS) is planning to provide open-access real-time ionospheric products. By now, the Centre National d’Etudes Spatiales (CNES) is the only IGS analysis center (AC) to broadcast real-time ionospheric vertical total electron content (VTEC) message through its real-time service (RTS). The quality of the CNES real-time ionospheric products is drawing increasing attention from the GNSS community. We evaluate the quality of CNES real-time VTEC message both in the ionospheric correction domain and positioning domain. First, 374 consecutive days of CNES VTEC products are collected and compared with the IGS final global ionospheric map (GIM) products. Second, slant total electron content (STEC) computed with CNES VTEC message is fully assessed with respect to STEC derived from dual-frequency GNSS measurements. Finally, RT-SF-PPP is conducted for assessing the quality of CNES real-time ionospheric products in the positioning domain. The degree and order of the spherical harmonic expansions broadcasted in the CNES VTEC messages changed from 6 to 12 in the time span of collected data, the effects of higher degree and order parameters are investigated at the same time in the experiments above.

Precise point positioning (PPP) provides a precise navigation solution with world-wide coverage using a single GNSS receiver. Single-frequency (SF) PPP has gained more interest in the recent years because of the low-cost of SF-GNSS receivers and their wide applications in the mass market. Real-time SF-PPP is now possible with the availability of both commercial and free real-time precise augmentation corrections. The two major sources of freely available real-time corrections are International GNSS Service real-time service (IGS-RTS) and GNSS augmentation systems such as the satellite-based augmentation system (SBAS). Profound Positioning Inc. (PPI) has developed a real-time SF-PPP technology known as “Instant PPP”. This paper demonstrates the capability of the instant PPP technology to work with the freely available real-time PPP corrections through static and kinematic analysis. The instant PPP was tested with corrections from two different IGS-RTS streams and two SBAS systems. The static test utilized six IGS stations located in North America, Europe and Asia. Furthermore, a kinematic road test is carried out in a suburban area with several overpass bridges. The results from both static and kinematic tests showed that instant PPP with precise corrections can achieve half-meter level horizontal accuracy and one-meter accuracy in the vertical direction in static and suburban scenarios.

Satellite clock offsets prediction is crucial for GNSS applications and has attracted much attention from the GNSS community. However, previous satellite clock offset prediction was mostly carried out based on the IGS rapid products or IGS final products. Limited by the long latency of the above products, the predicted satellite clock offset cannot meet the requirements of high precision real-time applications such as real-time PPP. In this paper, a new satellite clock offsets prediction method based on the IGS real-time service (RTS) products is proposed, in which the satellite clock drifts from the broadcast ephemeris are used as the pseudo-observations. For the polynomial part, only clock drift and clock drift rate are estimated while the latest clock offsets are directly applied. The GPS satellite clock offsets are predicted all together by considering the datum change involved in the IGS combination process, which is observed in the IGS01 clock products. The results show that the standard deviations of the predicted IGS01 products are 1.408 ns and 0.079 ns for the traditional method and proposed method, respectively. For the IGS03 products, the corresponding standard deviations are 0.243 ns and 0.080 ns. The proposed satellite clock offset prediction method provides better clock prediction performance based on the IGS RTS products.

With the revitalization of GLONASS constellation, it becomes feasible to integrate the GLONASS into the conventional GPS-only real-time precise point positioning (PPP) processing to enhance system availability and reliability. As generation of real-time orbit corrections is a crucial part of the real-time PPP system, a high-precision GLONASS orbit prediction method is proposed and evaluated in this paper. First, the concept of a new real-time PPP system will be briefly introduced. Then, GLONASS orbit prediction method is presented with an emphasis on assessing the differences of the full 9 parameters empirical CODE orbit model (ECOM) solar radiation pressure (SRP) model and the reduced 5 parameters ECOM SRP model. Finally, the generated orbits are compared with the observed part of the GFZ ultra-rapid products. Furthermore, the orbit quality is assessed in both static and kinematic PPP experiments. It is shown that an average accuracy for 12 h orbit prediction using the full ECOM model are 0.019, 0.085, and 0.029 m in the radial, along-track and cross-track direction, respectively. The average accuracy of static PPP positioning for 5 global IGS stations are 0.019, 0.019, 0.031 m in the east, north and up direction, respectively; while the average accuracy of kinematic PPP is 0.136, 0.090, 0.256 m in the east, north and up direction, respectively. Meanwhile, utilization of the reduced 5 parameters ECOM solar radiation pressure model will not degrade the orbit prediction accuracy significantly and therefore comparable positioning performance can be achieved.

The international GNSS service (IGS) has been providing an open-access real-time service (RTS) since 2013, which allows users to carry out real-time precise point positioning (RT-PPP). As the availability of RTS products is vital for RT-PPP, a disruption in receiving RTS products will be a concern. Currently, the IGS Ultra-rapid (IGU) orbit is accurate enough to be used as an alternative orbit for RTS during RTS outages, while the precision of the IGU predicted clock offsets is far below that of the RTS clock product. The existing clock prediction methods based on received RTS clock data will not work well if the discontinuity arises shortly after the start of the RT-PPP processing due to the lack of RTS clock data to fit the prediction model or to predict clock offsets at a high precision. Even if there is a sufficient amount of RTS clock data available, saving large amounts of RTS clock data would also use processor memory. An alternate approach for GPS clock prediction is proposed. The prediction model, composed of linear polynomial and sinusoidal terms, is similar to those used by the precious methods. The main innovation is the determination of the model coefficients: coefficients of linear and sinusoidal terms are estimated with the epoch-differenced clock offsets from the IGU observed part, while the constant coefficient is computed with the latest RTS clock corrections. There is no need to save the received RTS clock corrections, and clock prediction can be carried out even with only one epoch of RTS data. Evaluation of the proposed method shows that the predicted clock offsets within a short period of prediction time, e.g., 5 min, are slightly worse than RTS clock data. Even when the predicted time reaches up to 1 h, the precision of the predicted clock offsets is still higher than that of IGU predicted clock offsets by about 50%.

This paper proposed the high-precision satellite orbit prediction process at the user end for the real-time precise point positioning (PPP) system. Firstly, the structure of a new real-time PPP system will be briefly introduced in the paper. Then, the generation of satellite initial parameters (IP) at the sever end will be discussed, which includes the satellite position, velocity, and the solar radiation pressure (SRP) parameters for each satellite. After that, the method for orbit prediction at the user end, with dynamic models including the Earth's gravitational force, lunar gravitational force, solar gravitational force, and the SRP, are presented. For numerical integration, both the single-step Runge-Kutta and multi-step Adams-Bashforth-Moulton integrator methods are implemented. Then, the comparison between the predicted orbit and the international global navigation satellite system (GNSS) service (IGS) final products are carried out. The results show that the prediction accuracy can be maintained for several hours, and the average prediction error of the 31 satellites are 0.031, 0.032, and 0.033 m for the radial, along-track and cross-track directions over 12 h, respectively. Finally, the PPP in both static and kinematic modes are carried out to verify the accuracy of the predicted satellite orbit. The average root mean square error (RMSE) for the static PPP of the 32 globally distributed IGS stations are 0.012, 0.015, and 0.021 m for the north, east, and vertical directions, respectively; while the RMSE of the kinematic PPP with the predicted orbit are 0.031, 0.069, and 0.167 m in the north, east and vertical directions, respectively.

Chemically controlling crystal structures in nanoscale is challenging, yet provides an effective way to improve catalytic performances. Pt-based nanoframes are a new class of nanomaterials that have great potential as high-performance catalysts. To date, these nanoframes are formed through acid etching in aqueous solutions, which demands long reaction time and often yields ill-defined surface structures. Herein we demonstrate a robust and unprecedented protocol for facile development of high-performance nanoframe catalysts using size and crystallographic facet-controlled PtNi

A straightforward procedure for removing commonly used surfactants in nanoparticle synthesis, PVP and oleylamine/oleic acid, from Pt nanocubes by electrochemical potential cycling in 0.5 M NaOH is reported. The cyclic voltammetric results demonstrate that this procedure can effectively remove surfactants from Pt nanocubes, while preserving their surface structure. Keywords: Pt nanocubes, Electrochemical cleaning, Cyclic voltammogram, PVP, Oleylamine, Oleic acid