Oxygenate-induced structural evolution of high-entropy electrocatalysts for multifunctional alcohol electrooxidation integrated with hydrogen production.

High-entropy compounds have been emerging as promising candidates for electrolysis, yet their controllable electrosynthesis strategy remains a formidable challenge because of the ambiguous ionic interaction and codeposition mechanism. Herein, we report a oxygenates directionally induced electrodeposition strategy to construct high-entropy materials with amorphous features, on which the structural evolution from high-entropy phosphide to oxide is confirmed by introducing vanadate, thus realizing the simultaneous optimization of composition and structure. The representative P-CoNiMnWVOx shows excellent bifunctional catalytic performance toward alkaline hydrogen evolution reaction and ethanol oxidation reaction (EOR), with small potentials of -168 mV and 1.38 V at 100 mA cm-2, respectively. In situ spectroscopy illustrates that the electrochemical reconstruction of P-CoNiMnWVOx induces abundant Co-O species as the main catalytic active species for EOR and follows the conversion pathway of the C2 product. Theoretical calculations reveal the optimized electronic structure and adsorption free energy of reaction intermediates on P-CoNiMnWVOx, thereby resulting in a facilitated kinetic process. A membrane-free electrolyzer delivers both high Faradaic efficiencies of acetate and H2 over 95% and superior stability at100 mA cm-2 during 120 h electrolysis. In addition, the unique composition and structural advantages endow P-CoNiMnWVOx with multifunctional catalytic activity and realize multipathway electrosynthesis of formate-coupled hydrogen production.

'Beyond Li-Ion Technology' - A status review.

Li-ion battery is currently considered to be the most proven technology for energy storage systems when it comes to the overall combination of energy, power, cyclability and cost. However, there are continuous expectations for cost reduction in large-scale applications, especially in electric vehicles and grids, alongside growing concerns over safety, availability of natural resources for lithium, and environmental remediation. Therefore, industry and academia have consequently shifted their focus towards "beyond Li-ion technologies". In this respect, other non-Li-based alkali-ion/polyvalent-ion batteries, non-Li-based all solid-state batteries, fluoride-ion/ammonium-ion batteries, redox-flow batteries, sand batteries and hydrogen fuel cells etc. are becoming potential cost-effective alternatives. While there has been notable swift advancement across various materials, chemistries, architectures, and applications in this field, a comprehensive overview encompassing high-energy "beyond Li-ion" technologies, along with considerations of commercial viability, is currently lacking. Therefore, in this review article, a rationalized approach is adopted to identify notable 'post-Li' candidates. Their pros and cons are comprehensively presented by discussing the fundamental principles in terms of material characteristics, relevant chemistries, and architectural developments that make a good high-energy 'beyond Li' storage system. Furthermore, a concise summary outlining the primary challenges of each system is provided, alongside the potential strategies being implemented to mitigate these issues. Additionally, the extent to which these strategies have positively influenced the performance of these 'post-Li' technologies is discussed.

Development of an online hydrogen fuel quality analyzer with gas chromatography-pulsed discharge helium ionization detector for applying hydrogen infrastructures.

Hydrogen fuel, which is essential for the hydrogen economy, including hydrogen cell vehicles, must be of high quality for optimal hydrogen cell use. Currently, hydrogen fuel quality control is mainly done by offline analysis with periodic sampling. However, with the anticipated surge in hydrogen charging stations, there's a pressing need for cost-effective, high-throughput online analysis systems. Additionally, the miniaturization of these analytical instruments for field application is also a challenge. In this study, we present a compact, real-time hydrogen fuel analyzer based on gas chromatography with a pulsed discharge helium ionization detector. Its dual-column system efficiently analyzes major impurities in hydrogen fuel in less than 30 min. Indicator species (CO, CO2, CH4, O2, N2, and additional hydrogen sulfide [H2S]) are determined by examining hydrogen production and supply processes. The analyzer's measurement capability is consistent with µmol/mol-level analysis, providing valuable real-time information for hydrogen infrastructure managers. Additionally, it can analyze H2S, a crucial marker of sulfur compounds acting as catalytic poisons in fuel cells. This real-time analyzer offers efficient, informed decision-making support for hydrogen infrastructure managers, enhancing the overall reliability of hydrogen fuel in fuel-cell electric vehicles.

Role of chicken fat waste and hydrogen energy ratio as the potential alternate fuel with nano-additives: Insights into resources and atmospheric remediation process.

The main focus of the study was to witness the effects of chicken waste-based biodiesel blends along with constant hydrogen injection in a modified diesel engine. Furthermore, the nanoparticle multiwall carbon nanotubes (MWCNT) effects on the engine efficiency were also examined. A series of tests was conducted in the single cylinder, water cooled engine fuelled with diesel, CB100N, CB10N, CB30N, and CB50N. Throughout the entire run, constant hydrogen injection of 5 LPM has been maintained. The parameters such as brake thermal efficiency, brake specific fuel consumption, heat release rate and the emissions of different pollutants were determined for a variety of engine speeds. ASTM standards were applied to measure the viscosity, density and calorific value. From the reported findings, it was clear that the addition of the chicken waste biodiesel could be a sustainable substitute for the existing fossil fuels. Although the emission of the pollutants was dropped significantly, there was a massive drop in the BTE values. To compensate such shortage of power, the biodiesel was dispersed with MWCNT at the concentration of 80 ppm. Compared to the regular biodiesel, MWCNT inclusion increased the BTE by 14%. Further, the consumption of the fuel was also reduced marginally. Considering the pollutants, the catalytic activity of the MWCNT reduced the emissions of CO, NOx, and HC at various engine speeds. Besides, 10% reduction in NOx had been reported at lower engine speeds and was reduced to 8% at higher speed regimes. Compiling all together, increasing the concentration of the biodiesel blends obviously reduced the performance values and however, there was a great advantage in terms of the emission magnitudes irrespective of the engine operating conditions.

Advanced Energy Management Strategy of Photovoltaic/PEMFC/Lithium-Ion Batteries/Supercapacitors Hybrid Renewable Power System Using White Shark Optimizer.

The slow dynamic response of a proton exchange membrane fuel cell (PEMFC) to high load change during deficit periods must be considered. Therefore, integrating the hybrid system with energy storage devices like battery storage and/or a supercapacitor is necessary. To reduce the consumed hydrogen, an energy management strategy (EMS) based on the white shark optimizer (WSO) for photovoltaic/PEMFC/lithium-ion batteries/supercapacitors microgrid has been developed. The EMSs distribute the load demand among the photovoltaic, PEMFC, lithium-ion batteries, and supercapacitors. The design of EMSs must be such that it minimizes the use of hydrogen while simultaneously ensuring that each energy source performs inside its own parameters. The recommended EMS-based-WSO was evaluated in regard to other EMSs regarding hydrogen fuel consumption and effectiveness. The considered EMSs are state machine control strategy (SMCS), classical external energy maximization strategy (EEMS), and optimized EEMS-based particle swarm optimization (PSO). Thanks to the proposed EEMS-based WSO, hydrogen utilization has been reduced by 34.17%, 29.47%, and 2.1%, respectively, compared with SMCS, EEMS, and PSO. In addition, the efficiency increased by 6.05%, 9.5%, and 0.33%, respectively, compared with SMCS, EEMS, and PSO.

PEMFCs Model-Based Fault Diagnosis: A Proposal Based on Virtual and Real Sensors Data Fusion.

Proton Exchange Membrane Fuel Cells (PEMFCs) are critical components in renewable hybrid systems, demanding reliable fault diagnosis to ensure optimal performance and prevent costly damages. This study presents a novel model-based fault diagnosis algorithm for commercial hydrogen fuel cells using LabView. Our research focused on power generation and storage using hydrogen fuel cells. The proposed algorithm accurately detects and isolates the most common faults in PEMFCs by combining virtual and real sensor data fusion. The fault diagnosis process began with simulating faults using a validated mathematical model and manipulating selected input signals. A statistical analysis of 12 residues from each fault resulted in a comprehensive fault matrix, capturing the unique fault signatures. The algorithm successfully identified and isolated 14 distinct faults, demonstrating its effectiveness in enhancing reliability and preventing performance deterioration or system shutdown in hydrogen fuel cell-based power generation systems.

The alternative path for fossil oil: Electric vehicles or hydrogen fuel cell vehicles?

New energy vehicles are accelerating to substitute for internal combustion engine vehicles (ICEVs) and fossil oil. Although most literature acknowledges this trend, few compare two specific substitutable paths in terms of the operation system, namely electric vehicles (EVs) and hydrogen fuel cell vehicles (HFCVs). This paper makes a comparative analysis of EVs and HFCVs in power sources, fuel storage and transportation, fuel supply infrastructure construction, and the cost and use of vehicles. Our findings indicate that electric passenger vehicles have more advantages in economy, safety, and environmental impact, in comparison with hydrogen fuel cell passenger vehicles. Nevertheless, great efforts should still be made to develop advanced rapid charging technology, shorten charging time, and accelerate charging infrastructure construction. Then, it is just around the corner for EVs to gradually take over from traditional motor vehicles driven by oil. In contrast, popularizing hydrogen fuel cell passenger vehicles faces several insurmountable obstacles in the short run, such as the high hydrogen production price, complicated storage process, and expensive hydrogen refueling station infrastructure. However, hydrogen fuel cell commercial vehicles have unique application scenarios. The dislocation and complementarity principle in different scenarios of EVs and HFCVs is supposed to be firmly grasped.

Desalination Fuel Cells with High Thermodynamic Energy Efficiency.

Sustainably-produced hydrogen is currently intensively investigated as an energy carrier to replace fossil fuels. We here characterize an emerging electrochemical cell termed a desalination fuel cell (DFC) that can continuously generate electricity and desalinate water while using hydrogen and oxygen gases as inputs. We investigated two operational modes, a near-neutral pH operation with H2, O2, and feedwater inputs (H2|O2), and a pH-gradient mode with H2, O2, feedwater, acid, and base inputs (H2 + B|O2 + A). We show that our cell can desalinate water with 30 g/L of salt content to near-zero salt concentration, while generating an enormous amount of electricity of up to 8.6 kW h per m3 of treated water when operated in the pH-gradient mode and up to about 1 kW h per m3 for the near-neutral mode. We quantify the thermodynamic energy efficiency of our device in both operational modes, showing that significantly higher efficiency is achievable in the pH-gradient mode, with up to 95.6%. Further, we present results elucidating the key bottlenecks in the DFC process, showing that the cell current and voltage are limited in the near-neutral pH operation due to a lack of H+ to serve as a reactant, and further reinforce the deleterious effect of halide poisoning on the cathode Pt catalyst and cell open circuit voltage. Such findings demonstrate that new fuel cell catalyst materials, tailored for environments associated with water treatment, can unlock yet-improved performance.

Interaction-Dependent Interfacial Charge-Transfer Behavior in Solar Water-Splitting Systems.

Dual-band-gap systems are promising for solar water splitting due to their excellent light-harvesting capability and high charge-separation efficiency. However, a fundamental understanding of interfacial charge-transfer behavior in the dual-band-gap configuration is still incomplete. Taking CdS/reduced graphene oxide (CdS/RGO) nanoheterojunctions as a model solar water splitting system, we attempt here to highlight the interaction-dependent interfacial charge-transfer behavior based on both experimental observations and theoretical calculations. Experimental evidence points to charge transfer at the CdS-RGO interface playing a dominant role in the photocatalytic hydrogen production activity. By tuning the degree of reduction of RGO, the interfacial interaction, and, thereby, the charge transfer can be controlled at the CdS-RGO interface. This observation is supported by theoretical analysis, where we find that the interfacial charge transfer is a balance between the effective single-electron- and hole-transfer probability and the surface free electron and hole concentration, both of which are related to the surface potential and tailored by interfacial interaction. This mechanism is applicable to all systems for solar water splitting, providing a useful guidance for the design and study of heterointerfaces for high-efficiency energy conversion.

Hup-Type Hydrogenases of Purple Bacteria: Homology Modeling and Computational Assessment of Biotechnological Potential.

Three-dimensional structures of six closely related hydrogenases from purple bacteria were modeled by combining the template-based and ab initio modeling approach. The results led to the conclusion that there should be a 4Fe3S cluster in the structure of these enzymes. Thus, these hydrogenases could draw interest for exploring their oxygen tolerance and practical applicability in hydrogen fuel cells. Analysis of the 4Fe3S cluster's microenvironment showed intragroup heterogeneity. A possible function of the C-terminal part of the small subunit in membrane binding is discussed. Comparison of the built models with existing hydrogenases of the same subgroup (membrane-bound oxygen-tolerant hydrogenases) was carried out. Analysis of intramolecular interactions in the large subunits showed statistically reliable differences in the number of hydrophobic interactions and ionic interactions. Molecular tunnels were mapped in the models and compared with structures from the PDB. Protein-protein docking showed that these enzymes could exchange electrons in an oligomeric state, which is important for oxygen-tolerant hydrogenases. Molecular docking with model electrode compounds showed mostly the same results as with hydrogenases from E. coli, H. marinus, R. eutropha, and S. enterica; some interesting results were shown in case of HupSL from Rba. sphaeroides and Rvi. gelatinosus.

Portable Power Generation for Remote Areas Using Hydrogen Generated via Maleic Acid-Promoted Hydrolysis of Ammonia Borane.

A significant drawback to ammonia borane as a hydrogen storage material is the production of ammonia gas during hydrolysis. As a possible solution, maleic acid is shown to be capable of fully promoting hydrolysis of ammonia borane while also preventing ammonia release in excess of single digit parts per million. The reaction is shown to be relatively insensitive towards common water contaminants, with seawater, puddle water, and synthetic urine resulting in hydrogen evolution comparable to that observed when using highly pure deionized water. A common cola beverage was also investigated as a potential water source, with results deviating from those observed when using the other water sources. The ability to use low quality water sources presents the option of acquiring water at the point of use, greatly increasing the energy density of the system during transportation. For each of the water sources being used, concentrations of ammonia in the gas products of maleic acid-promoted hydrolysis were found to be less than the lower detection limits of the employed analysis methods. Based on this reaction, a portable hydrogen reactor is reported and shown to be capable of on-demand hydrogen generation sufficient to power a proton exchange membrane fuel cell at varying loads without significant changes in system pressure. The overall power production system has substantial value in scenarios where electrical power is required but there is no access to an established electrical utility, with prime examples including disaster relief and expeditionary military operations.

Dramatic increase in the oxygen reduction reaction for platinum cathodes from tuning the solvent dielectric constant.

Hydrogen fuel cells (FC) are considered essential for a sustainable economy based on carbon-free energy sources, but a major impediment are the costs. First-principles quantum mechanics (density functional theory including solvation) is used to predict how the energies and barriers for the mechanistic steps of the oxygen reduction reaction (ORR) over the fcc(111) platinum surface depend on the dielectric constant of the solvent. The ORR kinetics can be strongly accelerated by decreasing the effective medium polarizability from the high value it has in water. Possible ways to realize this experimentally are suggested. The calculated volcano structure for the dependence of rate on solvent polarization is considered to be general, and should be observed in other electrochemical systems.

Nickel foam supported Mn-doped NiFe-LDH nanosheet arrays as efficient bifunctional electrocatalysts for methanol oxidation and hydrogen evolution.

Electrochemical upgrading methanol into value-added formate at the anode in alkaline media enables the boosting production of hydrogen fuel at the cathode with saved energy. To achieve such a cost-effective and efficient electrocatalytic process, herein this work presents a Mn-doped nickel iron layered double hydroxides supported on nickel foam, derived from a simple hydrothermal synthesis. This developed electrocatalyst could act as an efficient bifunctional electrocatalyst for methanol-to-formate with a high faradaic efficiency of nearly 100 %, and for hydrogen evolution reaction, at an external potential of 1.5 V versus reversible hydrogen electrode. Additionally, a current density of 131.1 mA cm-2 with a decay of merely 12.2 % over 120 h continuous long-term testing was generated in co-electrocatalysis of water/methanol solution. Further density functional theoretical calculations were used to unravel the methanol-to-formate reaction mechanism arising from the doping of Fe and/or Mn. This work offers a good example of co-electrocatalysis to produce formate and green hydrogen fuel using a bifunctional electrocatalyst.

Advanced Architectures of Air Electrodes in Zinc-Air Batteries and Hydrogen Fuel Cells.

The air electrode is an essential component of air-demanding energy storage/conversion devices, such as zinc-air batteries (ZABs) and hydrogen fuel cells (HFCs), which determines the output power and stability of the devices. Despite atom-level modulation in catalyst design being recently achieved, the air electrodes have received much less attention, causing a stagnation in the development of air-demanding equipment. Herein, the evolution of air electrodes for ZABs and HFCs from the early stages to current requirements is reviewed. In addition, the operation mechanism and the corresponding electrocatalytic mechanisms of ZABs are summarized. In particular, by clarifying the air electrode interfaces of ZABs at different scales, several approaches to improve the air electrode in rechargeable ZABs are reviewed, including innovative electrode structures and bifunctional oxygen catalysts. Afterward, the operating mechanisms of proton-exchange-membrane fuel cells (PEMFCs) and anion-exchange-membrane fuel cells (AEMFCs) are explained. Subsequently, the strategies employed to enhance the efficiency of the membrane electrode assembly (MEA) in PEMFCs and AEMFCs, respectively, are highlighted and discussed in detail. Last, the prospects for air electrodes in ZABs and HFCs are considered by discussing the main challenges. The aim of this review is to facilitate the industrialization of ZABs and HFCs.

The Recent Progress of Oxygen Reduction Electrocatalysts Used at Fuel Cell Level.

Proton exchange membrane fuel cells (PEMFCs) are gaining significant interest as an attractive substitute for traditional fuel cells, with higher energy density, lower environmental pollution, and better operation efficiency. However, the cathode reaction, i.e., the oxygen reduction reaction (ORR), is widely proved to be inefficient, and therefore an obstacle to the widespread development of PEMFCs. The requirement for affordable highly-efficient ORR catalysts is extremely urgent to be met, especially at fuel cell level. Unfortunately, most previous reports focus on the ORR performance at rotating disk electrodes (RDE) level instead of membrane electrode assembly (MEA) level, making it harder to evaluate ORR catalysts operating under real vehicle conditions. Obviously, it is extremely necessary to develop an in-depth understanding of the structure-activity relationship of highly-efficient ORR catalysts applied at MEA level. In this work, an overview of the latest advances in ORR catalysts is provided with an emphasis on their performance at MEA level, hoping to cover the novel and systemic insights for innovative and efficient ORR catalyst design and applications in PEMFCs.

Unveiling CeZnOx Bimetallic Oxide: A Promising Material to Develop Composite SPPO Membranes for Enhanced Oxidative Stability and Fuel Cell Performance.

The incorporation of cerium-zinc bimetallic oxide (CeZnOx) nanostructures in sulfonated poly(2,6-dimethyl-1,4-phenylene oxide) (SPPO) membranes holds promise in an enhanced and durable fuel cell performance. This investigation delves into the durability and efficiency of SPPO membranes intercalated with CeZnOx nanostructures by varying the filler loading of 1, 2, and 3% (w/w). The successful synthesis of CeZnOx nanostructures by the alkali-aided deposition method is confirmed by wide-angle X-ray diffraction spectroscopy (WAXS), Raman spectroscopy, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analyses. CeZnOx@SPPO nanocomposite membranes are fabricated using a solution casting method. The intricate interplay of interfacial adhesion and coupling configuration between three-dimensional CeZnOx and sulfonic moieties of the SPPO backbone yields an enhancement in the bound water content within the proton exchange membranes (PEMs). This constructs simultaneously an extensive hydrogen bonding network intertwined with the proton transport channels, thereby elevating the proton conductivity (Km). The orchestrated reversible redox cycling involving Ce3+/Ce4+ enhances the quenching of aggressive radicals, aided by Zn2+, promoting oxygen deficiency and Ce3+ concentration. This synergistic efficacy ultimately translates into composite PEMs characterized by a mere 4% mass loss and a nominal 6% decrease in Km after rigorous exposure to Fenton's solution. Remarkably, an improved power density of 403.2 mW/cm2 and a maximum current density of 1260.6 mA/cm2 were achieved with 2% loading of CeZnOx (SPZ-2) at 75 °C and 100% RH. The fuel cell performance of SPZ-2 is 74% higher than its corresponding pristine SPPO membrane.

Ultrafine nickel-rhodium nanoparticles anchored on two-dimensional vanadium carbide for high performance hydrous hydrazine decomposition at mild conditions.

The development of heterogeneous supported nanocatalysts with a high kinetics combined with low cost is off importance but remains still challenged for hydrazine hydrate served as a promising hydrogen storage material. Herein, by virtue of surficial functional groups, ultrafine NiRh NPs were monodispersed on the two-dimensional V2C surface via a conventional wet chemical co-reduction. The optimized NiRh/V2C system demonstrates an excellent catalytic performance toward selectively catalyzing dehydrogenation of hydrazine hydrate, affording 100% H2 selectivity with the turnover frequency (TOF) value of 987.5 h-1 at 323 K. Such an enhancement is mainly attributed to synergistic effect of nanosystem, which will optimize local surface energy and promote electron transfer in NiRh/V2C system, thereby improving the kinetic selectivity of catalytic hydrazine hydrate decomposition. This work has provided a facile strategy for developing nanocatalysts with high kinetics that could enable huge industrial applications in the future.

Brookite TiO2 as an active photocatalyst for photoconversion of plastic wastes to acetic acid and simultaneous hydrogen production: Comparison with anatase and rutile.

Photoreforming is a clean photocatalytic technology for simultaneous plastic waste degradation and hydrogen fuel production, but there are still limited active and stable catalysts for this process. This work introduces the brookite polymorph of TiO2 as an active photocatalyst for photoreforming with an activity higher than anatase and rutile polymorphs for both hydrogen production and plastic degradation. Commercial brookite successfully converts polyethylene terephthalate (PET) plastic to acetic acid under light. The high activity of brookite is attributed to good charge separation, slow decay and moderate electron trap energy, which lead to a higher generation of hydrogen and hydroxyl radicals and accordingly enhanced photo-oxidation of PET plastic. These results introduce brookite as a stable and active catalyst for the photoconversion of water contaminated with microplastics to value-added organic compounds and hydrogen.

A Comparative Analysis of Friction and Energy Losses in Hydrogen and CNG Fueled Engines: Implications on the Top Compression Ring Design Using Steel, Cast Iron, and Silicon Nitride Materials.

Optimizing the design of the top compression ring holds immense importance in reducing friction across both traditional Internal Combustion (IC) engines and hybrid power systems. This study investigates the impact of alternative fuels, specifically hydrogen and CNG, on the behavior of top piston rings within internal combustion (IC) engines. The goal of this approach is to understand the complex interplay between blow-by, fuel type, material behavior, and their effects on ring friction, energy losses, and resulting ring strength. Two types of IC engines were analyzed, taking into account flow conditions derived from in-cylinder pressures and piston geometry. Following ISO 6622-2:2013 guidelines, thick top compression rings made from varying materials (steel, cast iron, and silicon nitride) were investigated and compared. Through a quasi-static ring model within Computational Fluid Dynamics (CFD), critical tribological parameters such as the minimum film and ring friction were simulated, revealing that lighter hydrogen-powered engines with higher combustion pressures could potentially experience approximately 34.7% greater power losses compared to their heavier CNG counterparts. By delving into the interaction among the fuel delivery system, gas blow-by, and material properties, this study unveils valuable insights into the tribological and structural behavior of the top piston ring conjunction. Notably, the silicon nitride material demonstrates promising strength improvements, while the adoption of Direct Injection (DI) is associated with approximately 10.1% higher energy losses compared to PFI. Such findings carry significant implications for enhancing engine efficiency and promoting sustainable energy utilization.

Improved super-twisting sliding mode control strategy in permanent magnet synchronous motors for hydrogen fuel cell centrifugal compressor.

This paper rigorously addresses the intricate control demands of high-speed, high-pressure, wide adjustable speed range, and high energy utilization efficiency required in hydrogen fuel cell centrifugal compressor, with a focus on the speed control of 40,000 RPM permanent magnet synchronous motors (PMSMs). An improved second-order super twisting sliding mode control (STSMC) strategy is proposed to enhance system stability and robustness by integrating the beetle antennae search (BAS) algorithm and grey wolf optimization (GWO) algorithm. The global search capability of BAS is used to improve the local optima issues of GWO, and then the improved GWO algorithm is utilized to address the issues related to parameter selection and convergence speed inherent in the STSMC. Theoretical validity of the proposed strategy is asserted through Quadratic Lyapunov Function, and its practicality is affirmed by thorough simulation. Comparative analyses are conducted with PI controller, traditional Sliding Mode Controller (SMC), and standard Super-Twisting Sliding Mode Controller (ST) under several case studies to show the superiority of the propose STSMC.