Publications

This paper presents a comparative analysis of two hydrogen station configurations during the refueling process: the conventional “directly pressurized refueling process” and the innovative “cascade refueling process.” The objective of the cascade process is to refuel vehicles without the need for booster compressors. The experiments were conducted at the Hydrogen Research and Fueling Facility located at California State University Los Angeles. In the cascade refueling process the facility buffer tanks were utilized as high-pressure storage enabling the refueling operation. Three different scenarios were tested: one involving the cascade refueling process and two involving compressor-driven refueling processes. On average each refueling event delivered 1.6 kg of hydrogen. Although the cascade refueling process using the high-pressure buffer tanks did not achieve the pressure target it resulted in a notable improvement in the nozzle outlet temperature trend reducing it by approximately 8 ◦C. Moreover the overall hydrogen chiller load for the two directly pressurized refuelings was 66 Wh/kg and 62 Wh/kg respectively whereas the cascading process only required 55 Wh/kg. This represents a 20% and 12% reduction in energy consumption compared to the scenarios involving booster compressors during fueling. The observed refueling range of 150–350 bar showed that the cascade process consistently required 12–20% less energy for hydrogen chilling. Additionally the nozzle outlet temperature demonstrated an approximate 8 ◦C improvement within this pressure range. These findings indicate that further improvements can be expected in the high-pressure region specifically above 350 bar. This research suggests the potential for significant improvements in the high-pressure range emphasizing the viability of the cascade refueling process as a promising alternative to the direct compression approach.

Hydrogen is envisioned to become a fundamental energy vector for the decarbonization of energy systems. Two key factors that will define the success of hydrogen are its sustainability and competitiveness with alternative solutions. One of the many challenges for the proliferation of hydrogen is the creation of a sustainable supply chain. In this study a methodology aimed at assessing the economic feasibility of holistic hydrogen supply chains is developed. Based on the designed methodology a tool which calculates the levelized cost of hydrogen for the different stages of its supply chain: production transmission & distribution storage and conversion is proposed. Each stage is evaluated individually combining relevant technical and economic notions such as learning curves and scaling factors. Subsequently the findings from each stage are combined to assess the entire supply chain as a whole. The tool is then applied to evaluate case studies of various supply chains including large-scale remote and small-scale distributed green hydrogen supply chains as well as conventional steam methane reforming coupled with carbon capture and storage technologies. The results show that both green hydrogen supply chains and conventional methods can achieve a competitive LCOH of around €4/kg in 2030. However the key contribution of this study is the development of the tool which provides a foundation for a comprehensive evaluation of hydrogen supply chains that can be continuously improved through the inputs of additional users and further research on one or more of the interconnected stages.

Low-carbon hydrogen could be an important component of a net-zero carbon economy helping to mitigate emissions in a number of hard-to-abate sectors. The United States recently introduced an escalating production tax credit (PTC) to incentivize production of hydrogen meeting increasingly stringent embodied emissions thresholds. Hydrogen produced via electrolysis can qualify for the full subsidy under current federal accounting standards if the input electricity is generated by carbon-free resources but may fail to do so if emitting resources are present in the generation mix. While use of behind-the-meter carbon-free electricity inputs can guarantee compliance with this standard the PTC could also be structured to allow producers using grid-supplied electricity to qualify subject to certain clean energy procurement requirements. Herein we use electricity system capacity expansion modeling to quantitatively assess the impact of grid-connected electrolysis on the evolution of the power sector in the western United States through 2030 under multiple possible implementations of the clean hydrogen PTC. We find that subsidized grid-connected hydrogen production has the potential to induce additional emissions at effective rates worse than those of conventional fossil-based hydrogen production pathways. Emissions can be minimized by requiring grid-based hydrogen producers to match 100% of their electricity consumption on an hourly basis with physically deliverable ‘additional’ clean generation which ensures effective emissions rates equivalent to electrolysis exclusively supplied by behind-the-meter carbon-free generation. While these requirements cannot eliminate indirect emissions caused by competition for limited clean resources which we find to be a persistent result of large hydrogen production subsidies they consistently outperform alternative approaches relying on relaxed time matching or marginal emissions accounting. Added hydrogen production costs from enforcing an hourly matching requirement rather than no requirements are less than $1 kg−1 and can be near zero if clean firm electricity resources are available for procurement.

Hydrogen embrittlement (HE) remains a pressing issue in materials science and engineering given its significant impact on the structural integrity of metals and alloys. This exhaustive review aims to thoroughly examine HE covering a range of aspects that collectively enhance our understanding of this intricate phenomenon. It proceeds to investigate the varied effects of hydrogen on metals illustrating its ability to profoundly alter mechanical properties thereby increasing vulnerability to fractures and failures. A crucial section of the review delves into how different metals and their alloys exhibit unique responses to hydrogen exposure shedding light on their distinct behaviors. This knowledge is essential for customizing materials to specific applications and ensuring structural dependability. Additionally the paper explores a diverse array of models and classifications of HE offering a structured framework for comprehending its complexities. These models play a crucial role in forecasting preventing and mitigating HE across various domains ranging from industrial settings to critical infrastructure.

While the share of renewable energy sources increased within the last years with an ongoing upward trend the energy sector is facing the problem of storing large amounts of electrical energy properly. To compensate daily and seasonal fluctuations a sufficient storage system has to be developed. The storage of hydrogen in the subsurface referred to as Underground Hydrogen Storage (UHS) shows potential to be a solution for this problem. Hydrogen produced from excess energy via electrolysis is injected into a subsurface reservoir and withdrawn when required. As hydrogen possesses unique thermodynamic properties many commonly used correlations can not be simply transferred to a system with a high hydrogen content. Mixing processes with the present fluids are essential to be understood to achieve high storage efficiencies. Additionally in the past microbial activity e.g. by methanogenic archaea was observed leading to a changing fluid composition over time. To evaluate the capability of reservoir simulators to cover these processes the present study establishes a benchmark scenario of an exemplary underground hydrogen storage scenario. The benchmark comprises of a generic sandstone gas reservoir and a typical gas storage schedule is defined. Based on this benchmark the present study assesses the capabilities of the commercial simulator Schlumberger ECLIPSE and the open-source simulator DuMux to mimic UHS related processes such as hydrodynamics but also microbial activity. While ECLIPSE offers a reasonable mix of user-friendliness and computation time DuMux allows for a better adjustment of correlations and the implementation of biochemical reactions. The corresponding input data (ECLIPSE format) and relevant results are provided in a repository to allow this simulation study’s reproduction and extension.

To meet the global climate goals agreed upon regarding the Paris Agreement governments and institutions around the world are investigating various technologies to reduce carbon emissions and achieve a net-negative energy system. To this end integrated solutions that incorporate carbon utilization processes as well as promote the transition of the fossil fuel-based energy system to carbon-free systems such as the hydrogen economy are required. One of the possible pathways is to utilize CO2 as the base chemical for producing a liquid organic hydrogen carrier (LOHC) using CO2 as a mediating chemical for delivering H2 to the site of usage since gaseous and liquid H2 retain transportation and storage problems. Formic acid is a probable candidate considering its high volumetric H2 capacity and low toxicity. While previous studies have shown that formic acid is less competitive as an LOHC candidate compared to other chemicals such as methanol or toluene the results were based on out-of-date process schemes. Recently advances have been made in the formic acid production and dehydrogenation processes and an analysis regarding the recent process configurations could deem formic acid as a feasible option for LOHC. In this study the potential for using formic acid as an LOHC is evaluated with respect to the state-of-the-art formic acid production schemes including the use of heterogeneous catalysts during thermocatalytic and electrochemical formic acid production from CO2 . Assuming a hydrogen distribution system using formic acid as the LOHC each of the production transportation dehydrogenation and CO2 recycle sections are separately modeled and evaluated by means of techno-economic analysis (TEA) and life cycle assessment (LCA). Realistic scenarios for hydrogen distribution are established considering the different transportation and CO2 recovery options; then the separate scenarios are compared to the results of a liquefied hydrogen distribution scenario. TEA results showed that while the LOHC system incorporating the thermocatalytic CO2 hydrogenation to formic acid is more expensive than liquefied H2 distribution the electrochemical CO2 reduction to formic acid system reduces the H2 distribution cost by 12%. Breakdown of the cost compositions revealed that reduction of steam usage for thermocatalytic processes in the future can make the LOHC system based on thermocatalytic CO2 hydrogenation to formic acid to be competitive with liquefied H2 distribution if the production cost could be reduced by 23% and 32% according to the dehydrogenation mode selected. Using formic acid as a LOHC was shown to be less competitive compared to liquefied H2 delivery in terms of LCA but producing formic acid via electrochemical CO2 reduction was shown to retain the lowest global warming potential among the considered options.

Proposals for achieving net-zero emissions by 2050 include scaling-up electrolytic hydrogen production however this poses technical economic and environmental challenges. One such challenge is for policymakers to ensure a sustainable future for the environment including freshwater and land resources while facilitating low-carbon hydrogen production using renewable wind and solar energy. We establish a country-by-country reference scenario for hydrogen demand in 2050 and compare it with land and water availability. Our analysis highlights countries that will be constrained by domestic natural resources to achieve electrolytic hydrogen self-sufficiency in a net-zero target. Depending on land allocation for the installation of solar panels or wind turbines less than 50% of hydrogen demand in 2050 could be met through a local production without land or water scarcity. Our findings identify potential importers and exporters of hydrogen or conversely exporters or importers of industries that would rely on electrolytic hydrogen. The abundance of land and water resources in Southern and Central-East Africa West Africa South America Canada and Australia make these countries potential leaders in hydrogen export.

This study describes the optimization of a modelling process concerning biogas’ use to generate green hydrogen and electrical power. The Aspen Plus simulation tool is used to model the procedure and the approach employed to limit the emissions of gas from the hydrogen production process will be the CO2 capture method. This technique uses slack lime (Ca(OH)2) to absorb CO2 capture since it is readily available. The study analyzes many critical parameters in the process including the temperature and pressure in the steam reforming (SR) and the water gas shift (WGS) reactions along with the steam to carbon ratio (S/C) to determine how the production of green hydrogen and electrical power will be influenced. Electricity generation is achieved by taking the residual water from the SR WGS carbonation reactions and converting it to the vapour phase allowing the steam to pass through the turbine to generate electricity. To examine the effects of the synchronized critical parameters response surface methodology (RSM) was used thus allowing the optimal operational conditions to be determined in the form of an optimized zone for operation. The result of parameter optimization gave the maximum green hydrogen production of 211.46 kmol/hr and electric power production of 2311.68 kWh representing increases of 34.86% and 5.62% respectively when using 100 kmol/hr of biogas. In addition control structures were also built to control the reactors’ temperature in the dynamic section. The tuning parameters can control the SR and WGS system’s reactor to maintain the system in approximately 0.29 h and 0.32 h respectively.

This work presents the design and application of two control techniques—a model predictive control (MPC) and a proportional integral derivative control (PID) both in combination with a multilayer perceptron neural network—to produce hydrogen gas on-demand in order to use it as an additive in a spark ignition internal combustion engine. For the design of the controllers a control-oriented model identified with the Hammerstein technique was used. For the implementation of both controllers only 1% of the overall air entering through the throttle valve reacted with hydrogen gas allowing maintenance of the hydrogen–air stoichiometric ratio at 34.3 and the air–gasoline ratio at 14.6. Experimental results showed that the average settling time of the MPC controller was 1 s faster than the settling time of the PID controller. Additionally MPC presented better reference tracking error rates and standard deviation of 1.03 × 10−7 and 1.06 × 10−14 and had a greater insensitivity to measurement noise resulting in greater robustness to disturbances. Finally with the use of hydrogen as an additive to gasoline there was an improvement in thermal and combustion efficiency of 4% and 0.6% respectively and an increase in power of 545 W translating into a reduction of fossil fuel use.

The main purpose of this article is to provide a short review of proton exchange membrane electrolyzer (PEMEL) modeling used for power electronics control. So far three types of PEMEL modeling have been adopted in the literature: resistive load static load (including an equivalent resistance series-connected with a DC voltage generator representing the reversible voltage) and dynamic load (taking into consideration the dynamics both at the anode and the cathode). The modeling of the load is crucial for control purposes since it may have an impact on the performance of the system. This article aims at providing essential information and comparing the different load modeling.