Future Energy Conversion Systems Research Articles

Smart utilization of bimetallic NiCo alloy supported carbon dots and sulfur quantum dots derived 3D nanocomposite for oxygen evolution reaction

The increasing demand for highly active and stable electrocatalysts for the oxygen evolution reaction (OER) in future energy-conversion systems has driven researchers to explore novel alternatives to Pt-based catalysts. Among these alternatives, zero-dimensional quantum dots have emerged as promising candidates due to their high surface area and intrinsic electrocatalytic activity, which lead to significant breakthroughs in electrocatalytic performance. Herein, we conducted a preliminary investigation into the application of bimetallic NiCo alloy deposited on metal-free quantum dots (carbon dots and sulfur quantum dots) derived nano sponge for the oxygen evolution reaction. The synthesized NiCo-CDs-800 exhibited remarkable electrocatalytic OER activity, achieving a current density of 10 mA cm−2 with only 221 mV overpotential, far surpassing commercial RuO2 electrocatalysts. The excellent electrocatalytic activity can be attributed primarily to high electrochemically active area (168.97 mF cm−2), the presence of large proportion of oxygen vacancies (68.61 %), rich pyridinic nitrogen structure (29.30 %) with strong water adsorption, and synergistic effect of bimetals as supported by density functional theory calculations. Meanwhile, the newly prepared NiCo-SQDs-700 under the similar procedure demonstrate a satisfied OER performance and competing stability when compared to NiCo-CDs. These findings open a new avenue for the application of metal free CDs and SQDs to the growing family of metal@QDs.

Thermodynamic evaluation and optimization of supercritical CO2 Brayton cycle considering recuperator types and designs

The recompression supercritical carbon dioxide Brayton cycle (SCO2-BC) has great potential for bottoming cycles among future energy conversion systems with comparatively high thermal efficiency. However, the recuperator type selections and optimal designs are a long-standing bottleneck of realizing maximum cycle efficiency and minimum cost. Reasonable collocation of recuperator types remains challenging. In this study, the thermodynamic–economic evaluation and optimization of recompression cycle were performed considering different recuperator types and designs. Printed circuit recuperator channel types include straight, zigzag, S-shaped, and airfoil fins. The design parameters include recuperator enthalpy efficiency and recompression fraction. The results indicate that low-temperature recuperator (LTR) with zigzag channel and high-temperature recuperator (HTR) with zigzag channel exhibit the best comprehensive cycle performance. The cycle thermal efficiency is more sensitive to the HTR enthalpy efficiency compared with the LTR. There is a local inflection point of the recompression fraction where the cycle efficiency is maximum and the exergy loss is minimum. The optimal solution of three-objective optimization considering efficiency, total cost, and exergy loss is more comprehensive than that of the two-objective optimization considering efficiency and cost. In the application of concentrated solar power, the annual carbon dioxide emission can be directly reduced by 0.43 Gt through this optimization improvement. The results of the current study offer a promising route to high-efficiency and low-cost applications of SCO2-BC by rational selection of recuperator types and designs.

A novel flow field design with flow re-distribution for advanced thermal management in Solid oxide fuel cell

Solid oxide fuel cell (SOFC) is an alternative for future energy conversion systems with great potential. Long-term operation in SOFC mainly obstructs its further development. Stratification and fission can be occurred in Positive electrolyte negative (PEN) structure by severe thermal stress. By improving the temperature uniformity, localized hot spots and thermal stresses can be eliminated significantly. This study proposed a novel rotary l-type main flow field for SOFC and the thermal and flow characteristics are investigated. The temperature distribution (TD) is estimated by the temperature uniformity index. The results show that the temperature uniformity index increased at least by 40%. The largest TG of the rotary l-type flow field is 20% lower than that of co-flow and cross-flow arrangements. The average TG is 32.72% lower than the counter-flow arrangement. This flow field design provides an effective solution for the long-term operation of SOFC.

Review of chemical looping process for carbonaceous feedstock Conversion: Rational design of oxygen carriers

• Metal oxides as oxygen carriers and corresponding performances in the chemical looping partial oxidation process for hydrogen/syngas production are summarized. • The regulation strategies for further improving reactivity and cycling stability are discussed. • The ion diffusion and surface reactions are anatomized via theory calculations and characterizations. The chemical looping partial oxidation (CLPO) process as a technology of chemical looping process (CLP) is recognized as a potential strategy for the efficient and clean conversion of fuels into syngas/H 2 . Herein, in view of the importance of low-cost high-performance metal oxides as oxygen carriers (OCs) for this conversion, we systematically review the classification and CLPO applications of such OCs and discuss the improvement of OC reactivity and stability via the creation of metal–metal or metal–support synergism, the generation of oxygen vacancies, and the enhancement of deactivation resistance. Further, we present the results of theoretical and experimental characterizations probing ion diffusion and surface reactions to provide insights into the related reaction mechanisms and touch on the challenges and opportunities of developing metal oxides with excellent reactivity and long-term cycling stability in CLP. Thus, this review facilitates the design and performance regulation of OCs for future energy conversion systems.

Performance evaluation of a solid oxide fuel cell multi-stack combined heat and power system with two power distribution strategies

Solid oxide fuel cell (SOFC) combined heat and power (CHP) system is a promising candidate for future energy conversion systems. Large power SOFC-CHP system needs multi-stack fuel cell (MFC) to solve the problems of thermal stress and system stability because MFC systems can achieve better performances for maximum power output and average efficiency than single stack fuel cell systems. This study develops an energy management strategy (EMS) for a SOFC multi-stack CHP system coupled with a methane reformer. SOFC multi-stacks are connected in parallel and verified by the published results. The effect of pressure and temperature on the overall multi-stack CHP system electrical efficiency and heat power is investigated with chain and adaptive EMS. The results show that as temperature and pressure increase, the system power increases. The temperature is more effective for the multi-stack system peak efficiency. Up to 11% of electrical system efficiency can be improved when the temperature rises from 700 °C (973 K) to 900 °C (1173 K). However, higher pressure reduces the peak efficiency by 1.5%. Both temperature and pressure can enlarge the output power range. The proposed model can serve as an effective solution for optimizing the SOFC multi-stack CHP system running on methane.

Facile preparation of sugarcane bagasse-derived carbon supported MoS2 nanosheets for hydrogen evolution reaction

Increasingly, future energy conversion systems highly demands non-noble metal catalysts with high activity and low cost for hydrogen evolution reaction (HER). This paper reports the use of waste sugarcane bagasse (SCB)-derived biomass carbon (SCBC) to synthesize carbon-supported molybdenum disulfide (MoS2) nanosheets for HER activity. The MoS2 nanosheets are uniformly loaded on the SCBC and show a vertical growth trend. Together, a synergistic effect was produced that impacted HER activity. The obtained MoS2/SCBC 2:1 showed admirable HER electrochemical activity, with a minimum overpotential of 142 mV at 10 mA cm−2, Tafel slope of 71 mV·dec-1 and Cdl value of 65.26 mF cm−2. The MoS2/SCBC 2:1 catalyst also exhibited high stability under acidic conditions. In conclusion, a non-noble metal electrocatalyst with low-cost and high-activity for HER from biomass waste has been provided for energy conversion system.

Investigation of electrochemical performance of an efficient Ti2O3–CeO2 nanocomposite for enhanced pollution-free energy conversion applications

The development of an economical, abundant, stable, and greatly active electrocatalyst for water oxidation is extremely important for future energy conversion system. Electrochemical water splitting is a new move toward H2 and O2 gas production. It can be used in sustainable and pollution-free energy conversion applications. In this work, Ti2O3–CeO2 nanocomposites were successfully synthesized with different molar ratios by facile hydrothermal method for electrochemical water oxidation. Mixed phase structure of Ti2O3–CeO2 nanocomposites was confirmed by X-ray diffraction spectra and well identified by highest peak of Ti2O3 in 2θ values of 33.0 and CeO2 in 2θ values of 28.5. The characteristic peaks from Raman and photoluminescence spectroscopy further confirmed Ti2O3–CeO2 nanocomposite formation. Existence of multidimensional nanostructures such as nanoparticles and small nanocubes of Ti2O3–CeO2 nanocomposites were investigated by scanning electron microscope images. Mesoporous nature of Ti2O3–CeO2 nanocomposites was further analyzed by Brunauer–Emmett–Teller analysis. The high surface area could benefit the Ti2O3–CeO2 nanocomposites with greatly improved oxygen evolution reaction (OER) performance. In three molar ratios, 1:3 M ratios of Ti2O3–CeO2 nanocomposites showed high catalytic action at overpotential of 244 mV. The best OER electrocatalyst was obtained by 1:3 M ratios of Ti2O3–CeO2 nanocomposites, which exhibited high current density and high specific capacitance values of 238 mA/g and 517 F/g, respectively. Therefore, Ti/Ce molar ratio played a crucial role in enhancing the OER performance.

Ru catalyst supported on nitrogen-doped nanotubes as high efficiency electrocatalysts for hydrogen evolution in alkaline media.

Due to the potential application in the future energy conversion system, there is an increasing demand for efficient, stable and cheap platinum-free catalysts for hydrogen evolution. However, it is still a great challenge to develop electrocatalysts with high activity similar to platinum or even higher, especially those that can work under alkaline conditions. Ruthenium (Ru), as a cheap substitute for platinum, has been studied as a feasible substitute for (HER) catalyst for hydrogen evolution reaction. In this paper, we designed and developed a novel Ru catalyst (Ru@CNT) supported on nitrogen-doped carbon nanotubes. Electrochemical tests show that even under alkaline conditions (1 M KOH), Ru@CNT still shows excellent catalytic performance and good durability. It only needs 36.69 mV overpotential to reach a current density of 10 mA cm−2, and its Tafel slope is 28.82 mV dec−1. The catalytic performance of the catalyst is comparable to that of 20% Pt/C. The significant activity is mainly attributed to the chelation of highly dispersed ruthenium atoms on nitrogen-doped carbon nanotubes. Secondly, the one-dimensional pore structures supported by nitrogen heterocarbon nanotubes can provide more opportunities for active centers. Excellent HER performance makes Ru@CNT electrocatalyst have a broad application prospect in practical hydrogen production.

Colloidal Synthesis of NiWSe Nanosheets for Efficient Electrocatalytic Hydrogen Evolution Reaction in Alkaline Media.

Searching for efficient, low-cost, and durable electrocatalysts toward the hydrogen evolution reaction (HER) is extremely urgent for future energy conversion systems. Herein, the colloidal synthesis of 2D tungsten-doped nickel selenide nanosheets by using Ni(acac)2 (acac=aceylacetonate), [W(CO)6 ], and selenium powder as precursors in oleylamine is reported. The introduction of tungsten is essential for the formation of 2D nanosheets. As a result, by taking the advantage of the unique layered structure and strong synergistic electronic effect between nickel, tungsten, and selenium, the as-synthesized Ni0.54 W0.26 Se nanosheets exhibit superior catalytic activity toward the HER in alkaline media, with an overpotential of 162 mV (η10 ), which is much lower than those of NiSe2 (η10 =330 mV) and WSe2 (η10 =378 mV), and higher than that of most previously reported selenide-based electrocatalysts.

Carbon-Quantum-Dots-Loaded Ruthenium Nanoparticles as an Efficient Electrocatalyst for Hydrogen Production in Alkaline Media.

Highly active, stable, and cheap Pt-free catalysts for the hydrogen evolution reaction (HER) are facing increasing demand as a result of their potential use in future energy-conversion systems. However, the development of HER electrocatalysts with Pt-like or even superior activity, in particular ones that can function under alkaline conditions, remains a significant challenge. Here, the synthesis of a novel carbon-loaded ruthenium nanoparticle electrocatalyst (Ru@CQDs) for the HER, using carbon quantum dots (CQDs), is reported. Electrochemical tests reveal that, even under extremely alkaline conditions (1 m KOH), the as-formed Ru@CQDs exhibits excellent catalytic behavior with an onset overpotential of 0 mV, a Tafel slope of 47 mV decade-1 , and good durability. Most importantly, it only requires an overpotential of 10 mV to achieve the current density of 10 mA cm-2 . Such catalytic characteristics are superior to the current commercial Pt/C and most noble metals, non-noble metals, and nonmetallic catalysts under basic conditions. These findings open a new field for the application of CQDs and add to the growing family of metal@CQDs with high HER performance.

Construction of uniform Co-Sn-X (X = S, Se, Te) nanocages with enhanced photovoltaic and oxygen evolution properties via anion exchange reaction.

The development of highly efficient electrocatalysts has attracted increasing attention in the field of electrochemical energy conversion. Therefore, we report a simple self-template method to construct Co-Sn-X (X = S, Se, Te) nanocages through the anion exchange reaction of CoSn(OH)6 nanocubes with chalcogenide ions under mild solvothermal conditions. Benefiting from advantageous compositional features and well-designed architectures, the obtained Co-Sn-X (X = S, Se, Te) nanocages display enhanced electrocatalytic activity for dye-sensitized solar cells (DSSCs) and the oxygen evolution reaction (OER) in an alkaline electrolyte. Remarkably, the Co-Sn-Se nanocages as the counter electrode (CE) catalyst deliver a prominent power conversion efficiency (PCE) of 9.25% for DSSCs compared with Pt CE (8.19%). Furthermore, when used as an OER catalyst, the Co-Sn-Se nanocages also exhibit outstanding electrocatalytic activity in terms of their low overpotential of 304 mV at the current density of 10 mA cm-2 and long-term stability in 1.0 M KOH solution. This work provides wide prospects for the rational design and synthesis of high-performance transition metal chalcogenide-based electrocatalysts for future energy conversion systems.

RuP2 -Based Catalysts with Platinum-like Activity and Higher Durability for the Hydrogen Evolution Reaction at All pH Values.

Highly active, stable, and cheap Pt-free catalysts for the hydrogen evolution reaction (HER) are under increasing demand for future energy conversion systems. However, developing HER electrocatalysts with Pt-like activity that can function at all pH values still remains as a great challenge. Herein, based on our theoretical predictions, we design and synthesize a novel N,P dual-doped carbon-encapsulated ruthenium diphosphide (RuP2 @NPC) nanoparticle electrocatalyst for HER. Electrochemical tests reveal that, compared with the Pt/C catalyst, RuP2 @NPC not only has Pt-like HER activity with small overpotentials at 10 mA cm-2 (38 mV in 0.5 m H2 SO4 , 57 mV in 1.0 m PBS and 52 mV in 1.0 m KOH), but demonstrates superior stability at all pH values, as well as 100 % Faradaic yields. Therefore, this work adds to the growing family of transition-metal phosphides/heteroatom-doped carbon heterostructures with advanced performance in HER.

基于燃料电池的储能电池系统的热能管理研究进展

能源存储系统是有效利用当前清洁能源/电能的主要途径之一。可逆燃料电池系统，作为高效的能量转换系统，已经在国际上引起广泛关注。然而，基于燃料电池系统进行清洁电能可逆存储，还需要满足商业化要求的80%的能量循环效率。本论文综述了当前燃料电池系统能量管理的最新研究进展，并对高温燃料电池系统的能量管理提出了研究方向。 Energy storage system is effective for current clean and renewable electricity utilization/storage. Reversible fuel cell system, as an efficient future energy conversion system, has been attracting a lot of attentions in the world. However, the reversible storage of clean electric energy based on fuel cell system also needs to meet the commercial requirements of 80% of the energy efficiency. This paper reviews the latest research progress in energy management of the fuel cell system, and the research direction of the energy management of high temperature fuel cell system is presented.

Seebeck Coefficient Characterization of Highly Doped <I>n</I>- and <I>p</I>-Type Silicon Nanowires for Thermoelectric Device Applications Fabricated with Top-Down Approach

A silicon nanowire one-dimensional thermoelectric device is presented as a solution to enhance thermoelectric performance. A top-down process is adopted for the definition of 50 nm silicon nanowires (SiNWs) and the fabrication of the nano-structured thermoelectric devices on silicon on insulator (SOl) wafer. To measure the Seebeck coefficients of 50 nm width n- and p-type SiNWs, a thermoelectric test structure, containing SiNWs, micro-heaters and temperature sensors is fabricated. Doping concentration is 1.0 x 10(20) cm(-3) for both for n- and p-type SiNWs. To determine the temperature gradient, a temperature coefficient of resistance (TCR) analysis is done and the extracted TCR value is 1750-1800 PPM x K(-1). The measured Seebeck coefficients are -127.583 microV x K(-1) and 141.758 microV x K(-1) for n- and p-type SiNWs, respectively, at room temperature. Consequently, power factor values are 1.46 mW x m(-1) x K(-2) and 1.66 mW x m(-1) x K(-2) for n- and p-type SiNWs, respectively. Our results indicate that SiNWs based thermoelectric devices have a great potential for applications in future energy conversion systems.

The Thermodynamic Evaluation and Optimization of Fuel Cell Systems

Energy conversion today is subject to high thermodynamic losses. About 50% to 90% of the exergy of primary fuels is lost during conversion into power or heat. The fast increasing world energy demand makes a further increase of conversion efficiencies inevitable. The substantial thermodynamic losses (exergy losses of 20% to 30%) of thermal fuel conversion will limit future improvements of power plant efficiencies. Electrochemical conversion of fuel enables fuel conversion with minimum losses. Various fuel cell systems have been investigated at the Delft University of Technology during the past 20 years. It appeared that exergy analyses can be very helpful in understanding the extent and causes of thermodynamic losses in fuel cell systems. More than 50% of the losses in high temperature fuel cell (molten carbonate fuel cell and solid oxide fuel cell) systems can be caused by heat transfer. Therefore system optimization must focus on reducing the need for heat transfer as well as improving the conditions for the unavoidable heat transfer. Various options for reducing the need for heat transfer are discussed in this paper. High temperature fuel cells, eventually integrated into gas turbine processes, can replace the combustion process in future power plants. High temperature fuel cells will be necessary to obtain conversion efficiencies up to 80% in the case of large scale electricity production in the future. The introduction of fuel cells is considered to be a first step in the integration of electrochemical conversion in future energy conversion systems.

Electrochemical model for performance analysis of a tubular SOFC

Tubular solid oxide fuel cells (SOFC) are promising candidates for future energy conversion systems and expected to be applied widely for small-scale distributed generation to large-scale central station power plants because of their high electrical efficiency and high temperature exhaust gas utilization. This study presents an electrochemical model to determine the performance characteristics of tubular solid oxide fuel cell. Activation, ohmic and concentration polarizations are regarded as the major sources of irreversibility. The Butler-Volmer equation, Fick's law and Ohm's law are used to determine the polarization terms. Performance curves are simulated for single cell voltage and power under variable current density and validated with published experimental data for given operating conditions. All the variations of tubular SOFC's operational conditions such as operating pressure and temperature in the electrochemical processes is taken into consideration. The contribution of each polarization term to voltage losses is analysed with local characteristics such as pore size, electrolyte thickness and activation energy for evaluating the relative changes. Cell performance represented by cell voltage, power, efficiency and heat generation are analysed at its complete operating range, aiming at finding the set of optimal operating conditions maximizing the overall cell performance. As a conclusion from this study, the developed model is a simple and effective tool to analyse tubular SOFC in obtaining insight information about cell performance characteristics under different conditions.

Decentralised energy systems: state of the art and potentials

The increasing liberalisation of the energy market as well as the ecological and business environment of public heat and power supply are leading to a re-evaluation of established and innovative energy conversion systems. A more efficient usage of fossil and regenerative primary energy resources is to be achieved by decentralised systems providing combined heat and electrical power. This paper discusses the potentials and challenges of today's and future energy conversion systems.

An evaluation of future energy conversion systems including fuel cell

This paper offers a comparison among various vehicles when using fossil fuel and renewable energy sources. In the case of fossil fuel, 5 key factors were compared among the fuel cell electric vehicle (FCEV), internal combustion engine (ICE) vehicle, battery powered, and hybrid vehicles. Comparison factors were cruising range, carbon dioxide emissions, waste heat rejection, air pollutants, and noise. According to this comparison, hybrid, battery powered, and fuel cell electric vehicles offer better potentials than ICE vehicles. In the case of utilizing renewable energy, EV will become the mainstream among vehicles types; FCEV will play an important role until that time. In this work, a high efficiency FCEV was designed from the viewpoint of fuel efficient utilization. This vehicle not only has a fuel cell, but also various energy utilization and storage systems, with excellent fuel economy of over 100km/l. The proposed FCEV will be very useful in mitigating urban and global warming, and in reducing fossil fuel consumption.

Quantum Well Thermoelectric Devices

ABSTRACTThis paper discloses the recent developments of high efficiency quantum well thermoelectrics at Hi-Z Technology, Inc. The performance of the latest P type B4C/B9C- N-type Si/SiGe couple will be presented as well as data for the new N-type Si/SiC that will replace Si/SiGe and improve couple efficiency.Preliminary calculations regarding the development of actual quantum well modules will be presented for power prediction. These modules can be used in future energy conversion system as well as air conditioning system designs.Our current efforts to produce quantum well films more rapidly will be discussed.

An Evaluation of Future Energy Conversion Systems Including Fuel Cell.

This paper presents a comparison among various vehicles when using fossil fuels and renewable energy. In case of using fossil fuel, we compared 5 key factors among the fuel cell electric vehicle (FCEV), internal combustion engine (ICE) vehicle (gasoline or diesel), battery-powered and hybrid vehicles. Comparison factors are cruising range, carbon dioxide (CO2) emissions, waste heat rejection, air pollutants and running noise. According to this comparison, hybrid, battery-powered and fuel cell electric vehicle have better potentials than ICE vehicles. In case of utilizing renewable energy, EV will become the mainstream among vehicles. In addition, FCEV will play an important role until that age. Moreover, we designed a high efficiency FCEV for the purpose of fuel effective utilization. This vehicle has not only fuel cell, but also various energy utilization and storage systems, for example battery, flywheel and PV cell. This vehicle has excellent fuel economy more than 90 km/l.