Green hydrogen & electricity production via geothermal-driven multi-generation system: Thermodynamic modeling and optimization

Mathematical modeling of an integrated photovoltaic-assisted PEM water electrolyzer system for hydrogen production

Proposal and assessment of a new geothermal-based multigeneration system for cooling, heating, power, and hydrogen production, using LNG cold energy recovery

The burgeoning demand for power across the globe and the disastrous effect of climate change that results from power generation through depleting unclean fuel sources have necessitated the use of renewable and clean fuels. Hydrogen is a good alternative but only when produced from low‐carbon energy resources. However, hydrogen production via this pathway has a high cost and low system efficiency. Therefore, a comparative cost analysis has been performed for hydrogen production through solar power tower (SPT) and parabolic trough collector (PTC) with proton exchange membrane (PEM) electrolyzer. This is carried out using different cycle configurations comprising a modified steam Rankine cycle (MSRC), supercritical carbon dioxide Brayton cycle (SCBC), and organic Rankine cycle (ORC). Optimization of the solar tower power configurations is also performed for improved system performance. The result of the analysis showed that all SPT’s configurations outperformed the PTC’s configurations except for the configuration comprising the steam Rankine cycle (SRC) and ORC due to how well it performed under the low operating temperature of the PTC system. The levelized cost of hydrogen (LCOH) ranged from 7.78 $/kg for the PTC‐MSRC‐ORC configuration to 17.76 $/kg for the PTC‐MSRC‐SCBC configuration. The parametric analysis of the system also showed that the capacity factor had the greatest influence on system performance. Furthermore, a multiobjective optimization of the system using a brute‐force algorithm for minimizing the LCOH and maximizing efficiency improved the system performance in all configurations.

Proton exchange membrane (PEM) water electrolysis offers significant potential for sustainable production of green hydrogen due to its high current density, superior hydrogen purity, and excellent conversion efficiency. However, widespread industrial implementation remains challenging because state-of-the-art oxygen evolution reaction (OER) catalysts heavily rely on iridium, a precious metal with limited global supply and high costs.1–4 Therefore, considerable research efforts have been dedicated to developing new catalysts requiring lower iridium loadings. Although PEM electrolysis typically operates at elevated temperatures (50-80°C),1 most studies assessing catalyst activity and stability have been performed at room temperature, and the limited available temperature-dependent studies primarily focus on alkaline environments.5,6 In this work, we have systematically investigated the temperature-dependent activity and stability of two representative Ir-based catalysts: a commercial IrO₂ catalyst and a supported core-shell Ir@IrOₓ catalyst. Using a high-temperature rotating-disk electrode (RDE) setup, electrochemical assessments of the activity and stability of the catalysts were performed across a range of operating temperatures from 20°C up to 80°C. We investigated how the increased operating temperature affects the OER activities of these two catalysts, observing not only enhanced kinetics with the increased working temperatures but also altered reaction mechanisms, as indicated by the Tafel analysis of the OER polarization curves. Furthermore, by employing an accelerated stress test protocol, we evaluated the stability of the two catalysts under varied temperatures. Comprehensive in-situ and post-mortem characterization techniques, including in-situ XRD, XPS (Figure 1), TEM, and ICP, were employed to investigate the structural changes of the catalysts during the stability tests, which revealed the accelerated degradation at higher working temperatures, but also the surprisingly high OER stability of the core-shell Ir@IrOx structure under high working temperatures.Figure 1: Comparison the Ir 4f XPS spectra of the sample before and after the stability test at 60 °C.References Carmo, M., Fritz, D. L., Mergel, J. & Stolten, D. A comprehensive review on PEM water electrolysis. Int J Hydrogen Energy 38, 4901–4934 (2013). Wang, C. & Feng, L. Recent advances and perspectives of Ir-based anode catalysts in PEM water electrolysis. Energy Advances 3, 14–29 (2024). Kibsgaard, J. & Chorkendorff, I. Considerations for the scaling-up of water splitting catalysts. Nature Energy 2019 4:6 4, 430–433 (2019). Reier, T., Oezaslan, M. & Strasser, P. Electrocatalytic oxygen evolution reaction (OER) on Ru, Ir, and pt catalysts: A comparative study of nanoparticles and bulk materials. ACS Catal 2, 1765–1772 (2012). Shi, G. et al. Temperature Dependence of Oxygen Evolution Reaction Activity in Alkaline Solution at Ni-Co Oxide Catalysts with Amorphous/Crystalline Surfaces. ACS Catal 12, 14209–14219 (2022). Lyu, X., Li, J., Yang, J. & Serov, A. Significance of slight ambient temperature variation on the electrocatalyst performance toward oxygen evolution reaction. J Environ Chem Eng 11, 111492 (2023). Figure 1

This study explores the use of solar energy to drive a novel multigeneration system that includes, power, heating, cooling, and hydrogen production. The proposed system undergoes a thorough evaluation from three essential perspectives: Energy, Exergy, and Economics. Unlike previous studies, in the proposed system, Ammonia-LiNO3 operated absorption refrigeration cycle is integrated with the Steam Rankine cycle (SRC), organic Rankine cycle (ORC), and proton exchange membrane (PEM) electrolyzer. The influence of climatic conditions; solar flux and ambient temperature is examined on exergy efficiency of sub-systems and the overall system. The system yields a net power generation of 640 kW, a cooling production rate of 425 kW, heating output of 4190 kW, and a hydrogen production rate of 160 kg/hr. These outcomes of sub-systems are associated with cost rate of 6.20 $/hr and pay-back period of 6.02 years at the baseline operation. The proposed multigeneration system achieved energy and exergy efficiencies of 23.31% and 6.25%. The solar flux experiences a positive effect on electricity generation and rate of hydrogen production. The exergy efficiency of sub-systems producing hydrogen, cooling, heating, and elec-tricity generation is obtained as 66.25%, 34.5%, 29.3%, and 69%, respectively, at ambient temperature of 25°C. The exergy efficiency of overall system increases approximately by 65% with increase of ambient temperature from 5 to 40°. Exergy analysis determined tower-solar collector responsible for highest destruction of solar exergy (47.34%), although main energy loss occurs in multigeneration system. The proposed system appears to be superi-or to conventional solar-based multi-carrier energy systems from exergy perspective.

Energy and economic analysis of geothermal–solar trigeneration systems: A case study for a hotel building in Ischia

Electricity and hydrogen co-production via scramjet multi-expansion open cooling cycle coupled with a PEM electrolyzer

Risk and 4E analyses and optimization of a novel solar-natural gas-driven polygeneration system based on Integration of Gas Turbine–SCO2–ORC-solar PV-PEM electrolyzer

Development and application of flexible integrated microsensor as real-time monitoring tool in proton exchange membrane water electrolyzer

Electrolysis – Proton-exchange membrane electrolyzer | Proton exchange membrane water electrolysis: State-of-the-art technique and systems

The global push towards cleaner energy sources has heightened the demand for high-performing, durable proton exchange membrane water electrolyzer (PEMWE) electrocatalysts. Green hydrogen, generated through water electrolysis powered by renewable energy, stands as a prominent solution in this endeavor to transition away from fossil fuels. Among various electrolyzer technologies, PEMWE systems currently offer the most competitive pathway for green hydrogen production. These systems typically employ a platinum on carbon supported (Pt/C) cathodic electrocatalyst for the hydrogen evolution reaction (HER) and an iridium oxide (IrOx) anodic electrocatalyst for the oxygen evolution reaction (OER). Efforts to enhance PEMWE performance primarily focus on improving the kinetics of the OER process, which accounts for the majority of activation overpotential during operation. To address cost concerns associated with IrOx, researchers are exploring alternative formulations, including doping with materials like niobium (Nb), aiming for comparable performance at reduced Ir loading [1], [2], [3]. It is argued that higher surface area and lower crystalline IrOx catalysts lead to lower activation overpotentials and enhanced durability, respectively. In this study, we investigate the performance of high-surface-area IrOx electrocatalysts (>200 m2/g) and Nb-doped IrOx variants, comparing them with commercially available benchmarks. Through rigorous examination utilizing Rotating Disk Electrode (RDE), Gas Diffusion Electrode (GDE) half-cell, and Membrane Electrode Assemblies (MEAs), we report on the performance and stability of our in-house prepared materials. Preliminary results examining various loadings of IrOx suggest that lower loadings lead to durable and active electrocatalyst layers. Our findings underscore the potential of Nb-doped IrOx as a cost-effective alternative for PEMWE electrocatalysts, offering promising advancements in the pursuit of efficient and sustainable hydrogen production.

Hydrogen production from proton exchange membrane (PEM) water electrolysis is attractive due to its simple and clean nature. Membrane and electrode assemblies (MEAs) of PEM electrolyzers typically use iridium (Ir) as an anode catalyst and Pt as a cathode catalyst. The durability of MEAs plays an essential role for the electrolyzers’ lifetime and cost. However, unlike the well-established MEA durability protocols of PEM fuel cells, there have been a lack of effective procedures for PEM electrolyzer MEA durability evaluation. The objective of this work is to establish a series of test protocols that can help to rapidly evaluate PEM electrolyzer MEA durability. Three testing approaches have been used in this work, which include high-voltage hold (>1.8 V), voltage cycling (1.4 to 1.8 V or 2.0 V), and constant low-current operations. The electrochemical surface area (ECSA) and polarization curves of the MEAs will be obtained after each test. Two categories of anode catalysts have been evaluated using the above durability test protocols: one is the commercial Ir black and the other is Ir supported on tungsten-doped titanium oxide (Ir/WxTi1-xO2) developed at Giner. The supported Ir/WxTi1-xO2 catalyst proves to possess 8-10 x higher mass activity than the Ir black. The MEAs made of these two anode catalysts have been evaluated at a variety of loading, low (0.1 mg/cm2), medium (0.4 mg/cm2) and high (1.0 mg/cm2). Figure 1 shows the durability of these two catalysts after voltage cycling from 1.4 V to 1.8 V: (a) 2 mg/cm2 Ir from Ir black; (b) 0.4 mg/cm2 Ir from Ir/WxTi1-xO2. It can be seen that at medium to high Ir loadings, these two catalysts demonstrates minimal performance decay after voltage cycling. The morphology and structure of MEAs after durability tests will be characterized to correlate to their performance and to elucidate their degradation mechanisms. Acknowledgement: The financial support is from the Department of Energy under the Contract Grant DE-SC0007471. Figure 1

Hydrogen production from proton exchange membrane (PEM) water electrolysis is attractive due to its simple and clean nature. However, the technology is expensive due to high materials cost for the catalysts, membrane, and bipolar plate. In most commercial processes, iridium (Ir) black is used as an oxygen evolution catalyst at the anode. A high Ir loading (>2mg/cm2) has to be used due to significant anode over-potential loss caused by sluggish kinetics of the oxygen evolution reaction.The objective of this work is to develop advanced Ir catalysts with enhanced catalytic activity that may lead to decreased Ir loading and/or increased energy efficiency. Two categories of catalysts are being investigated. One is iridium nanotube catalyst, which is synthesized via a porous alumina template.1 The template can be a commercially available anodized alumina membrane with a relatively uniform capillary pore structure. The template was coated with an iridium precursor by subliming iridium precursor at an appropriate temperature. The precursor was then reduced to iridium. The template support was removed by etching with 10% potassium hydroxide. A cross-section of the nanotubes produced by this process is shown in Figure 1. The average length of the Ir nanotubes is 5um and the diameter ranges from 250 – 400 nm with a wall thickness of ≤50 nm. Energy-dispersive X-rayanalysis suggests that the tubes are composed of iridium dioxide. The template pore size and process conditions are being varied to change the dimension of the Ir nanotubes. In addition to Ir nanotubes, Ir catalysts dispersed on a variety of corrosion-resistant substrates like titanium oxide and indium tin oxide (ITO) are also being developed. The Ir dispersion on these supports may reduce Ir particle size thus potentially enhancing its catalytic activity. Figure 2 shows the TEM image of Ir particles supported on TiO2nanowires with 30 w.t. % Ir loading.The RDE performance and the electrolyzer performance of these catalysts are being investigated and their comparison with commercial Ir black will be reported. Acknowledgement:The financial support is from the Department of Energy under the Contract Grant DE- DE-SC0007471. TEM was performed by Drs. Fan Gao and Zhiyong Gu at University of Massachusetts at Lowell. References Pivovar AB, et al. J Electrochem Soc, 160, F848-52 (2013).

In this paper, we present the studies carried out on electrolysis of aqueous methanol for hydrogen production in a proton exchange membrane (PEM) electrolyser with a novel porous flow field made of sintered metal powder. The obtained results showed that the use of porous flow field has a significant improvement in performance compared to a conventional groove flow field. This could be attributed to an increase in effective electrode area and to a reduction in diffusion polarization by using the porous material which enables the flow field to supply reactant evenly to the electrodes. Based on this performance improvement, the influence of operating conditions such as cell voltage and methanol concentration on hydrogen production was analyzed.

Hydrogen plays a significant role in the transition of the global energy system towards achieving net-zero emissions. According to the “Hydrogen for Net-Zero” report by Hydrogen Council and McKinsey & Company, the demand for clean hydrogen could reach 140 metric tons (MT) by 2030, with a further increase to 660 MT by 2050. For future high-volume production of green hydrogen, Proton Exchange Membrane Water Electrolysis (PEMWE) is a crucial technology due to its advantages of high-purity hydrogen, large operational current densities, and great energy conversion efficiency [1]. However, the use of precious metal-based catalysts for the sluggish oxygen evolution reaction (OER) on the anode side hinders the high-volume manufacturability of PEMWE. To ensure cost-effectiveness in large-scale PEMWE deployment for hydrogen production, developing strategies to reduce Iridium loading to 0.1 - 0.2 mg Ir/cm2 without compromising overall performance is essential. The challenge of reducing Ir loading also involves improving or maintaining the electrical contact between the catalyst layers and the substrate [2-3].Smoltek Hydrogen has made significant strides in achieving low iridium loading through our innovative Porous Transport Electrode (PTE) concept. This approach involves modifying a Porous Transport Layer (PTL) by growing vertically aligned Carbon Nanofibers (CNFs) using our in-house patented technology, efficiently increasing surface area [4]. Following this modification, a protective layer of corrosion-resistant and conductive material (e.g., Platinum) is applied to the CNFs. Subsequently, an OER catalyst layer is deposited utilizing a three-electrode cathodic electrodeposition method (Fig. 1a and 1b). The electrodeposited Ir catalyst exhibits strong adhesion to the CNF PTEs, resulting in a high electrical conductivity [5].In this work, we successfully reduced Ir loadings to 0.1 mg/cm2 in the PTE, demonstrating excellent mass activity in the half-cell tests (Fig. 1c). In the PEMWE tests, the polarization curves of electrodes with low Ir loading exhibited superior performance compared to cells with significantly higher Ir loading (Fig. 1d). The next step of our research involves conducting constant current durability tests for over 600 hours on PEMWE operation using low Ir loaded PTEs. The aim is to minimize degradation and overcome mass transport limitations, particularly at higher current densities.These unique PTEs developed by Smoltek Hydrogen, with CNF technology, maximize the electrode surface area and pave a new way to increase the utilization ratio of catalyst surface at a low loading amount, which makes it a competitive anode material in today’s PEMWE market. References https://www.iea.org/reports/hydrogen-2156#dashboardMöckl et al. J. Electrochem. Soc., 2022, 169, 064505.Bernt et al. Chem. Ing. Tech., 2020, 92, 31-39.https://www.smoltek.com/applications/electrolyzers/Krivina et al. Adv.Mater., 2022, 34, 2203033.https://publications.jrc.ec.europa.eu/repository/handle/JRC104045 Figure 1