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In the field of food and agriculture, fuel cell-based energy supply technology is gaining much attention for sustainable food systems with carbon neutrality by 2050. Previous studies have focused on the electricity balance using polymer electrolyte fuel cells (PEMFCs) without considering the temperature quality to maintain the environmental conditions required in smart farms. However, this study proposes a system that can provide all four energy sources (electricity, cooling, heating, and CO2) required by smart farms by using solid oxide fuel cells (SOFC), which can utilize high-quality heat. To confirm the feasibility of the proposed idea, we demonstrate the world's first 10 kW-class SOFC-based integrated system for a smart farm in Jinju, South Korea. The system's core components consist of a SOFC system, a hot thermal storage system, a cold thermal storage system, and a CO2 supply system. In this study, the applicability of the proposed system is verified by the experimental results of the effective production of cold and hot heat required by smart farms. In addition, the technical problems encountered during the demonstration are presented. In doing so, we suggest the direction of more economical and sustainable SOFC technology development for smart farm applications.

Liquid organic hydrogen carrier (LOHC) is a chemical hydrogen storage method that stores hydrogen in the form of liquid organics. Dibenzyltoluene (DBT) is a promising LOHC material due to its high storage density, low ignitability, and low cost. In this study, Pt/Al2O3 and Pt/CeO2 catalysts are synthesized using a combustion nanocatalyst synthesis method called the glycine nitrate process (GNP) to obtain high catalytic activity for the dehydrogenation of perhydro-dibenzyltoluene (H18-DBT). Pt/CeO2 exhibits much faster dehydrogenation than Pt/Al2O3, 80.5%/2.5 h versus 3.5%/2.5 h. To investigate the causes of the difference in the dehydrogenation rates, microstructural characterization by N2 physisorption, CO chemisorption and transmission electron microscopy analysis are conducted, and the catalytic activities are evaluated at various liquid hourly space velocities (LHSVs). The differences in dehydrogenation can be attributed to the mass transport of liquid H18-DBT into the catalyst pores being slow due to the small pores in Pt/Al2O3, which is a rarely addressed issue for other LOHC materials. This is because many LOHC materials are dehydrogenated at the gas phase, which has higher diffusivity than that of the liquid phase. Pt/CeO2 synthesized by the GNP is also compared with a commercial Pt/Al2O3 catalyst. The commercial Pt/Al2O3 catalyst shows a dehydrogenation of 17.8%/2.5 h, which is much slower than that of Pt/CeO2 synthesized by the GNP, at 80.5%/2.5 h.

Recently, hydrogen energy technologies attract attention as power systems. To develop hydrogen energy systems, hydrogen storage methods with high storage density and good safety are required. Liquid organic hydrogen carrier (LOHC) is one of the novel hydrogen storage technologies. LOHC has advantages of high storage density, good safety, and easy handling. In this study, a polymer electrolyte membrane fuel cell (PEMFC) stack is operated with hydrogen released from LOHC to evaluate the feasibility of the connected operation of the PEMFC stack and LOHC dehydrogenation reactor. Dibenzyltoluene (H0-DBT) is used as a LOHC material, and the dehydrogenation of perhydro dibenzyltoluene (H18-DBT) is conducted at 240–300 °C. Released hydrogen is purified by adsorbent of activated carbon to remove impurities. However, 100–1400 ppm of methane is observed after the purification, and the PEMFC stack power is reduced from 39.4 W to 39.0 W during the operation by hydrogen dilution and physical adsorption of methane. Then, to evaluate the irreversible damage, pure hydrogen was supplied to the PEMFC stack. The stack power is recovered to 39.4 W. It is concluded that the connected operation of the LOHC dehydrogenation reactor and PEMFC stack is feasible, and the activated carbon adsorbent can be a cost-effective purification method for LOHC.

Hydrogen storage within a metal hydride involves exothermic and endothermic processes for hydrogen absorption and desorption, respectively. In addition, the thermal conductivity of the particulate metal hydride (i.e., powder) after repeated absorption processes is extremely low compared to its bulk phase. Low heat conduction through the metal hydride powder makes the hydrogen charging slow; thus, appropriate thermal management is necessary to achieve the fast charging time with the maximum energy density. In this work, we propose a thermal design of a portable hydrogen storage system made of a 300-mL vessel by balancing the internal and external thermal resistances. A copper-mesh structure is employed inside the vessel for enhancing the effective thermal conductivity of metal hydride powder (i.e., reducing the internal thermal resistance). On the other hand, a compact fan is used for enhancing the forced convection heat transfer from the vessel (i.e., reducing the external thermal resistance). Consequently, a copper-mesh structure sacrificing 4.3% of the internal vessel volume was manufactured by following the thermal design. In addition, the effect of the proposed thermal design was confirmed by actual hydrogen-charging experiments that showed 73.5% reduction of the charging time.

As renewable energy sources account for a larger portion of power generation, a hydrogen energy storage system (HESS) attracts attention for large capacity energy storage. At HESS, surplus electricity is used to produce hydrogen, and it is stored in compressed hydrogen tanks, and the hydrogen is utilized to generate electricity when electricity demand is high. Recently, liquid organic hydrogen carrier (LOHC) is proposed for hydrogen storage. LOHC is one of the hydrogen storage methods in which hydrogen is stored by the reaction with aromatic compounds. By using LOHC systems, high hydrogen storage density, and good safety are achievable. In this study, 20 Nm3/h class LOHC system with dibenzyltoluene (DBT) is designed. For the system design, catalytic performance, NMR analysis, and vapor pressure of DBT are evaluated, and a LOHC system composed of hydrogenation, dehydrogenation reactors, condenser, and adsorbent is designed for future demonstration.

A novel concept for diesel fuel processing utilizing H2O2 is suggested to obtain the high-purity H2 required for air-independent propulsion using polymer electrolyte membrane fuel cells for use in submarines and unmanned underwater vehicles. The core components include 1) a diesel-H2O2 autothermal reforming (ATR) reactor to produce H2-rich gas, 2) a water-gas shift (WGS) reactor to convert CO to H2, and 3) a H2 separation membrane to separate only high-purity H2. Diesel and H2O2 can easily be pressurized as they are liquids. The application of the H2 separation membrane without a compressor in the middle of the process is thus advantageous. In this paper, the characteristics of pressurized ATR and WGS reactions are investigated according to the operating conditions. In both reactors, the methanation reaction is enhanced as the pressure increases. Then, permeation experiments with a H2 separation membrane are performed while varying the temperature, pressure difference, and inlet gas composition. In particular, approximately 90% of the H2 is recovered when the steam-separated rear gas of the WGS reactor is used in the H2 separation membrane. Finally, based on the experimental results, design points are suggested for maximizing the efficiency of the diesel-H2O2 fuel processor.

Fuel cell electric vehicles have recently experienced rising demand. The geographic coverage of hydrogen stations, however, is limited. This study proposes an on-site hydrogen production system that converts heavy naphtha to high-purity hydrogen for remote areas without convenient access to hydrogen. It includes a pressurized steam reformer (SR) to produce H2-rich gas and a catalytic membrane reactor (MR) to promote H2-producing reactions and permeate hydrogen. By utilizing the liquid-fuel infrastructure, this compact system can produce hydrogen effectively and make it more accessible. Our paper describes how we maximize the system's hydrogen output by investigating how the operating conditions affect each component. Various tests are performed to select the system's water-gas-shift catalyst (Fe–Cr) and determine the optimal temperatures of the SR (800 °C) and the MR (400 °C). The MR shows enhanced catalytic performance from hydrogen permeation or 1.63 times higher hydrogen output at 25 bar(g) than a reactor that contains only catalyst (no membrane). At this pressure, the MR has a maximum hydrogen output at different SR reformate compositions. The maximization is possible by incorporating Le Chatelier's principle and minimizing methanation. This work is important because it proposes a comprehensive method to maximize on-site hydrogen output and ensure the MR's stable operation.

Energy storage have attracted attention to compensate for the mismatches of electricity supply and demand caused by renewable energies. A regenerative hydrogen fuel cell (RHFC) system composed of an electrolyzer, hydrogen storage, and fuel cell is a promising large capacity energy storage technology. A liquid organic hydrogen carrier (LOHC) is considered for hydrogen storage technology because of its advantages of good safety, easy handling, and high storage density. In this original research, a comparative energetic study on LOHC and other hydrogen storage technologies was conducted using net energy analysis to quantitatively compare various hydrogen storage technologies. First, the basic RHFC system was modeled by a 0-dimensional simulation, and the system efficiency was analyzed. Then, a net energy analysis was conducted by evaluating energy stored on investment (ESOIe) values. The RHFC system with LOHC showed a higher ESOIe of 53 for weekly (

A profitable operation strategy of an energy storage system (ESS) could play a pivotal role in the smart grid, balancing electricity supply with demand. Here, we propose an AI-based novel arbitrage strategy to maximize operating profit in the electricity market composed of a grid operator (GO), an ESS, and customers (CUs). This strategy, the buying and selling of electricity to profit from a price imbalance, can also cause a peak load shift from on-peak to off-peak, a win-win approach for both the ESS operator (EO) and the GO. Particularly, to maximize the EO's profit and further reduce the GO's on-peak power, we introduce a stimulus-integrated arbitrage algorithm, providing an additional reward to the EO from the GO with different weights for each peak period. The algorithm consists of two parts: the first is recurrent neural network-based deep learning for overcoming the future uncertainties of electricity prices and load demands. The second is reinforcement learning to derive the optimal charging or discharging policy considering the grid peak states, the EO's profit, and CUs’ load demand. We find it significant that the suggested approach increases operating profit 2.4 times and decreases the on-peak power of the GO by 30%.

A novel technology of a diesel reformer that uses hydrogen peroxide is developed to obtain the hydrogen required for fuel cell air-independent propulsion for underwater applications, such as submarines and unmanned underwater vehicles. Diesel fuel could be a promising hydrogen source for underwater applications due to its high hydrogen density and its globally well-equipped infrastructure. An alternative oxidant, hydrogen peroxide (H 2 O 2 ), is applied to supply not only oxygen but also the water required for diesel autothermal (ATR) reforming. The proposed reformer does not require an additional heating device to supply heat for the vaporization of diesel or oxidant due to the exothermic nature of the ATR reaction and the heat of decomposition of H 2 O 2 . The effects of H 2 O 2 on diesel reforming were confirmed based on operating the engineering-scale (kW e -class) diesel-H 2 O 2 reformer. Undecomposed H 2 O 2 caused an excessively high temperature in the mixing zone and a corrosion effect in the reformer wall. To overcome these phenomena, we introduced a catalytic H 2 O 2 decomposer to fully decompose hydrogen peroxide into steam and oxygen. From this important step, we essentially eliminate side effects from undecomposed H 2 O 2 and retain a high reforming efficiency by utilizing the heat of decomposition of H 2 O 2 .

To operate fuel cells effectively in low-oxygen environments, such as in submarines and unmanned underwater vehicles, a hydrogen source with high hydrogen storage density is required. In this paper, diesel autothermal reforming (ATR) with hydrogen peroxide as an alternative oxidant is proposed as a hydrogen production method. Diesel fuel has higher hydrogen density than metal hydrides or other hydrocarbons. In addition, hydrogen peroxide can decompose into steam and oxygen, which are required for diesel ATR. Moreover, both diesel fuel and hydrogen peroxide are liquid states, enabling easy storage for submarine applications. Hydrogen peroxide exhibited the same characteristics as steam and oxygen when used as an oxidant in diesel reforming when pre-decomposition method was used. The thermodynamically calculated operating conditions were a steam-to-carbon ratio (SCR) of 3.0, an oxygen-to-carbon ratio (OCR) of 0.5, and temperatures below 700 °C to account for safety issues associated with hydrogen peroxide use and exothermic reactions. Catalytic activity and stability tests over Ni–Ru (19.5–0.5 wt.%)/Ce0.9Gd0.1O2−x were conducted using various diesel compounds. Furthermore, long-term diesel ATR tests were conducted for 200 h using Korean commercial diesel. The degradation rate was 3.67%/100 h without the production of ethylene.

잠수함 및 수중무인체계 등의 산소희박환경에서 연료전지를 통한 효과적인 전력생산을 위해서는 높은 수소저장밀도를 갖는 수소공급원이 필요하다. 디젤연료는 액체연료로서 저장 및 공급이 용이하며, 연료전지의 연료가 되는 수소의 단위질량 및 단위부피당 저장밀도가 높은 장점을 갖고 있다. 이러한 디젤연료의 장점을 기반으로 본 연구에서는 산소희박환경에서 수소생산을 위해 디젤연료의 개질반응을 이용하였으며, 산화제로 단위부피당 산소 저장밀도가 높고 액상으로 보관이 용이한 과산화수소 수용액을 기존의 산화제인 물과 산소의 대체산화제로 이용하는 방법을 제안하였다. 과산화수소 수용액의 디젤개질 산화제로써의 특성을 파악하기 위해 물, 공기 산화제와의 비교실험을 진행하였으며, 기존의 산화제와 디젤 개질반응 시 동일한 특성을 갖는 것을 실험적으로 확인하였다. 또한 상용디젤을 연료로 온도 및 과산화수소 수용액의 농도에 따른 개질성능을 평가하였으며, 49시간의 가속 열화실험을 통하여 디젤, 과산화수소 수용액을 이용한 수소생산의 가능성을 확인하였다.

A hydrogen energy storage system for portable/mobile applications such as personal power sources and unmanned underwater vehicles is developed. An application-oriented design and system integration strategy are newly suggested to maximize energy density while incorporating conventional technologies for the electrolyzer (Ely), the metal hydride (MH), and the polymer electrolyte membrane fuel cell (PEMFC). To improve both the energy density and usability, the systems for charging and discharging are separated. The charging component is composed of a water Ely (0.5 Nm3 h−1) and an MH cooling device as one system. The discharging component consists of an MH (900 NL H2), a PEMFC stack (50 W), and a power conditioning system (PCS) as a single system. The MH material and engineering properties are investigated to find an MH that is suitable for the target system. The hybrid design and operating strategy of the PEMFC and PCS are developed to maximize energy density. The prototype system provides a nominal power output of 31.5 W at 12 V for 38 h with one recharging. We find it significant that the discharging component shows an energy density of 410 Wh L−1, which is twice that of conventional energy storage systems at the 2.9-L level.

A diesel reformer start-up strategy using hydrogen peroxide (H2O2) decomposition heat is first proposed for subsea applications such as submarines and unmanned underwater vehicles (UUVs), requiring no oxygen. H2O2 can supply not only both the oxygen and steam required for the diesel autothermal reforming (ATR) reaction but also heat via the catalytic H2O2 decomposition reaction. We utilize the high-quality heat from H2O2 for the reformer start-up by evaporating and chemically decomposing the 50 wt% concentration H2O2. A comparative reformer start-up strategy study is performed between conventional diesel ATR and diesel-H2O2 ATR using a 1 kWe-class diesel reformer. For the conventional start-up, three steps of partial oxidation, partial load ATR, and full load ATR are required to heat the ATR reformer after electrically preheating the ATR catalyst. However, the proposed strategy requires only one full load ATR step after preheating the ATR catalyst using H2O2 decomposition heat. With the suggested start-up strategy, a simplified sequence with negligible temperature fluctuations and a 57% start-up time reduction are achieved. We find it significant that the full load flowrate of superheated steam generation from the H2O2 decomposer is a critical factor in simplifying and shortening the start-up procedure.