The pursuit of hydrogen energy presents a promising path toward meeting growing energy needs sustainably while addressing urgent climate issues. However, developing a hydrogen economy demands significant investments in advanced infrastructure for production, storage, and transportation. The use of critical minerals is essential at nearly every stage of hydrogen technology to ensure efficiency. Consequently, one of the key future challenges will be managing these minerals responsibly to prevent depletion. Phosphorus, for instance, plays a crucial role in research on liquid organic hydrogen storage systems and is becoming increasingly important in catalyst development for water splitting. As research in this field expands rapidly, the demand for phosphorus in hydrogen technology will inevitably rise. This review highlights phosphorus' significance in advancing hydrogen technology, covering its applications in heterogeneous photocatalysis, including black phosphorus, red phosphorus, transition metal phosphides, and emerging high-entropy phosphide materials, as well as phosphorus-doped supports for ammonia borane hydrolysis. In homogeneous catalysis, the review examines the role of phosphorus-based ligands in designing catalysts for liquid organic hydrogen carrier (LOHC) systems, particularly those involving carbon dioxide conversion into formic acid, formate, amides, and methanol. The review also addresses catalyst deactivation mechanisms, theoretical descriptors for rational catalyst design, and sustainable phosphorus management strategies including immobilization, durability, recovery, and efficiency metrics. By emphasizing phosphorus' vital contributions, this article aims to raise awareness of its role in the hydrogen economy, encourage its thoughtful integration into future technologies, and promote sustainable practices in its use.

Choosing an appropriate H2/O2 recombination catalyst is crucial for enhancing efficiency in hydrogen technologies. This study used density functional theory calculations to investigate PtxPd1-x (0 <= x <= 1) alloys with varying slab thicknesses and surface areas. The performance of these alloys and the reaction intermediates (O, H, OH, OH + H, H2O) formed on the catalyst surfaces for the H2/O2 recombination reaction was analysed. Catalytic activity of pristine Pd (111) and PtPd3, PtPd, Pt3Pd, and Pt7Pd (111) alloy surfaces was evaluated using adsorption and reaction energies. Stability was found along the (111) Miller index for all tested alloys. Strong surface adsorption was observed on PtPd (111) and PtPd3 (111) surfaces, while weaker adsorption occurred on Pt7Pd (111) surfaces. Lower activation energies were observed on Pt7Pd (111) and Pt3Pd (111) surfaces for the rate-determining step (O* + H* -> *OH), compared to pristine Pd (111). In contrast, the *OH formation step was inhibited on PtPd (111) and PtPd3 (111) surfaces due to strong surface absorption of reaction intermediates. Overall, Pt3Pd (111) and Pt7Pd (111) surfaces are promising alternative catalysts for H2/O2 recombination, especially in the rate-determining *OH formation step.

Dibenzyltoluene/perhydro-dibenzyltoluene (H0DBT/H18DBT) is considered a promising liquid organic hydrogen carrier (LOHC) pair for the storage and transportation of green hydrogen (H2). However, at the point of use, the catalytic dehydrogenation of H18DBT is still limited by mass transport limitations. To address this issue, the dehydrogenation of H18DBT was successfully conducted on Pt/Al2O3-coated foams in both an unstirred tank reactor and a fixed-bed reactor (FBR). A performance comparison between coated foams and pellets in the tank reactor revealed that H2 productivities were 12–59% higher in the foam-based reactor than in the pellet-based reactor. Since the textural properties of the foam-supported and pellet-based catalysts were similar, the higher degree of dehydrogenation (DoD) and H2 productivity achieved by the former were attributed to the geometric properties of the foam structure. Long-term tests performed in the FBR demonstrated the ability of the coated foams to maintain steady activity for >16 h on stream. However, the single-pass DoDs achieved were 34–38%. By recycling the partially dehydrogenated products three times into the FBR, the DoD improved to 63%. The results of this study demonstrated the capabilities of the coated foams in the process intensification of LOHC dehydrogenation reactors.

Passive autocatalytic recombiners (PARs) are essential safety systems used in nuclear power plants (NPPs) to prevent hydrogen explosions during severe accidents. This study investigates the operational behaviour of cylindrical-type catalysts used in a PAR. The study employs experimental and computational fluid dynamics (CFD) analyses to evaluate the catalyst temperature distribution and hydrogen conversion inside the PAR channel. Experimental analysis measures the hydrogen conversion of the catalyst and temperature distribution by means of hydrogen sensors and an infrared camera. The CFD analysis uses a three-dimensional (3D) model developed in STAR-CCM+ code to simulate the flow and recombination reaction in a cylindrical-type PAR catalyst section. Results indicated that the catalyst has decent conversion efficiency. Furthermore, the temperature over the catalyst section is evenly distributed and it does not exceed the lower hydrogen ignition limit. CFD analysis of the Schmidt number demonstrates that the flow inside the PAR is highly turbulent and Sct values is in the range of 0.2-0.28. It was found that the recombination reaction occurs in the diffusion regime. The recombination reaction primarily occurs in the catalyst's lower and central parts. Finally, this paper proposes the functional dependence to estimate the efficiency of the entire PAR based on the Sherwood equation and mechanistic transport approach. The results of this study provide crucial insight into the cylindrical-type catalyst operational behaviour in PARs and the CFD model design of cylindrical-type catalysts for the safety analysis of NPPs.

Nuclear energy appears to be a promising technology to replace fossil fuels in the foreseeable future. It is therefore important to develop accurate numerical models to ensure safe operation of nuclear power plants, especially during severe accident scenarios. Passive Autocatalytic Recombiners are currently employed to mitigate hydrogen explosions during accidents. Numerical modelling of Passive Autocatalytic Recombiners remains a multidimensional and Multiphysics problem that involves simulation of fluid dynamics, hetero-, and homogeneous chemistry, heat, and mass transport, and various necessary details in order to obtain reliable results. However, it is significant to outline the fundamental components of PAR modelling. This paper summarises the most popular approaches to PAR modelling and compares various studies to identify the differences and also highlights the similarities. This summary clearly shows the trends of the most recent development on the topic and identifies gaps for future work. Thus far, various models have been developed for steady state, low inlet hydrogen concentration (similar to 4%), low flow (velocity is similar to 1 m/s), dry air, and, only a few studied oxygen starvation and carbon monoxide poisoning. These models have proven to be accurate in the first approximation and have been validated by various test facilities. Nonetheless, there is still a large scope in developing models for transient and start-up behaviour, ignition criteria, other catalyst types, and higher hydrogen concentrations, temperatures, and pressures. These conditions are typical of accident scenarios at nuclear power plants and are therefore vital to predict accurately.

Electromagnetic induction heating could eliminate the limitations associated with conventional heating methods for endothermic dehydrogenation reactions of liquid organic hydrogen carriers-it may offer faster heating rates, while directing the heat from the core of the inductively active materials to the catalyst and the surrounding fluid. A 5 wt% Pt/gamma-Al2O3 prepared by wet impregnation, was used as a wash-coat to produce an inductively active catalyst in which stainless steel (SS) pellets were used. Different configurations were considered, for comparison: SS pellets alone, Pt/gamma-Al2O3 coated SS pellets, a mixture of 5 wt% Pt/gamma-Al2O3 pellets and SS pellets. An induction heating set-up for the catalytic dehydrogenation of perhydro-benzyltoluene (H12-BT) was built (use was made of an inductive coil covering a glass batch reactor. Increasing the n(Pt)/n(H12-BT) ratio lowered the catalyst productivity (gH(2)gPt(-1)min(-1)) by 7.4%, but enhanced the H12-BT conversion and selectivity towards the product benzyltoluene (H0-BT). Remarkably, there are no by-products in either the liquid or gas phases at high conversion (>90%).

A Pt-Co/Al2O3 bimetallic catalyst for catalytic hydrogen combustion (CHC) is prepared and its performance is evaluated. A colloidal dispersion of a Pt-sulphite complex is used as the Pt precursor instead of the conventional H2PtCl6 solution. The prepared catalyst maintains its catalytic activity at a temperature of up to 337 degrees C for 500 h of continuous CHC. To assess the catalytic activity and thermal conductivity of the catalyst, a catalytic cartridge for a recombiner section is designed. The thermal distribution over the catalytic surface during CHC is measured, using an infrared camera, as a function of inlet hydrogen concentration (0-10 vol%) and gas flow velocity (4-12 m/s). Hydrogen conversion is also determined, to evaluate the catalytic activity of the prepared catalysts. Results of this study indicate that the Pt reactive metal can be partially replaced with Co-thus reducing the cost of the catalyst, without diminishing the catalyst performance towards CHC.(c) 2023 The Authors. Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/).

The catalysts utilized for the dehydrogenation of dibenzyltoluene-based liquid organic hydrogen carriers (LOHCs) remain crucial. The state-of-the-art catalyst for dehydrogenation of dibenzyltoluene-based LOHC still suffers from deactivation and by-product formation. This is crucial in terms of the efficiency of the industrial dehydrogenation plant for hydrogen production, cyclability as well as the cost of replacing the catalyst. The development of catalysts with optimum performance, minimum deactivation and low by-product formation is required to attain the full benefits of the LOHC technology. Therefore, in this study, the effect of Mg and Zn modification on Pt/Al2O3 catalyst is investigated for the catalytic dehydrogenation of perhydro-dibenzyltoluene (H18-DBT). In addition, an assessment of reaction kinetics is also conducted. High dehydrogenation performance was obtained for Mg-doped Pt/Al2O3 using a batch reactor at 300 °C and 6 h reaction time. In this case, the degree of dehydrogenation (dod), productivity and conversion obtained are 100%, 1.84 gH2/gPt/min and 99.9%, respectively. Moreover, the Mg-doped catalyst has resulted in a high turnover frequency (TOF) of 586 min−1 compared to the Zn-doped catalyst (269 min−1) and the undoped catalyst (202 min−1) at the reaction temperature of 300 °C. The amount of by-products increased with an increase in the catalytic activity, with the Pt/Mg-Al2O3 catalyst possessing the highest amount of by-products. The dehydrogenation of H18-DBT followed first-order reaction kinetics. In addition, the activation energy obtained using the Arrhenius model is 102, 130 and 151 kJ/mol for Pt/Al2O3, Pt/Zn-Al2O3 and Pt/Mg-Al2O3, respectively. Although the Mg-doped Pt/Al2O3 shows high activation energy, the higher performance of the catalyst suggests that mass transfer limitations have no major effect on the dehydrogenation reaction under the conditions used.

Pt/Al2O3-coated Al foams were tested for the passive autocatalytic recombination of H-2. The characterisation of the washcoat surface confirmed the uniform distribution of Pt and Al2O3 over the entire washcoat surface. Transmission electron microscopy results revealed a slight increase in particle size from 3.8 to 6.2 nm after prolonged reaction. High H-2 conversions of 57-89% are achieved and the catalyst activity is maintained for >480 h on stream. The performance of the foam-based catalyst bed is similar to that of plates but surpasses that of catalyst pellets. Temperatures recorded at the hottest spots on the foam surface reach a maximum of only 393 degrees C at the highest H-2 inflow. Computational fluid dynamics simulations were performed on the actual foam geometry obtained using computed tomography. The simulations demonstrate the importance of thermal radiation in the model. There is good agreement between results of experimental H-2 conversions and maximum combustion temperatures.

For decades, proton-exchange membrane (PEM) water electrolysis (WE) has been mainly used for oxygen generation in anaerobic environments. Over the past two decades, however, it has been increasingly used for hydrogen generation in the industrial sectors at various scales. The PEMWE technology is also considered a key in the ongoing energy transition, if the process of hydrogen generation by means of WE is linked to renewable energy sources, such as wind, solar, etc. The following key elements enable the operation of a PEM WE plant for hydrogen production: a PEM-based WE stack and the balance of plant. The related system includes, but not limited to such key modules as the water and oxygen management systems, hydrogen gas management system, water input system, safety system, power electronics and electrolysis cell stack power supply, control system, and some other. A WE stack comprises several cells connected in series with electrically conductive bipolar plats and end plates. General design principles for the stack involve reducing efficiency losses, while aiming at lower costs and increase in durability. WE stacks should be designed in such a way, that an even current distribution is maintained, the water feed is optimized, suitable compression ratios are achieved, and preferably high discharge pressure of hydrogen can be enabled. For the stack level, in simple terms, efficiency is benchmarked by the total applied voltage, which includes the Nernst potential, anode and cathode overpotentials, and ohmic overpotentials due to the membrane ionic resistance and interfacial resistance at given current density. Overpotential represents inefficiencies in a cell stack, and some of stack design efforts focus on reducing these overpotential contributions. However, a compromise has to be found between (a) costs reduction challenges (that are often associated with the reduction of PGM-based catalyst loading, attempts to replace Ti as a key material for the bipolar plates, and the less expensive SPE membrane), (b) sufficient durability, (c) performance of the stack, (d) increase in power density of a stack. This talk will focus on the WE stack, and its subcomponents review, as well as characterization methods for both, a single cell and a stack and also challenges of the large-scale stack manufacturing. The key components of the WE stack include ion-conductive solid polyelectrolyte membranes (SPE), anode and cathode catalyst layers (CL), bipolar plates and current collectors/ gas diffusion layers (porous transport layers). In order to gain fundamental understanding of the relationships between electrical loses, degradation of the stack components and strategies to increase power density of the stacks, advanced characterization and modelling tools need to be used. These include, but not limited to electrochemical impedance spectroscopy (EIS), current interrupt (CI), dynamic compression measurements with piezoelectric senor plates, current mapping, gas cross-over analysis, computational fluid dynamics (CFD) simulations modelling, various visualization tools, etc. For example, CFD could assist in understanding and improving fluid flow dynamics in a WE stack as it is a complex challenge that requires a detailed examination of the geometry, channel design, and operating conditions within the stack. As for EIS, the usage of the distribution of relaxation times (DRT) approach would potentially allow to focus on the direct analysis of the data rather focusing on the equivalent circuit development. Approximately 15 years ago the South African Government approved a national program HySA: Hydrogen South Africa, which resulted in the development of the expertise and capacity to conduct research, development, and earlier commercial activities around green hydrogen production by means of water electrolysis. These activities include the development of local IP at the components, stack, and system levels.

For decades, proton-exchange membrane (PEM) water electrolysis (WE) has been used mainly for oxygen generation in anaerobic environments. Over the past two decades, however, it has been increasingly used for hydrogen generation in the industrial sector at various and increasing scale. The PEMWE technology is also considered as a key one in the frame of the ongoing energy transition if the process of hydrogen generation by means of WE is linked to renewable energy sources, such as wind, solar, etc. Among other existing water electrolysis technologies, such as alkaline, solid oxide, the technology based on proton-exchange membranes has received a great deal of interest in South Africa. One of the reasons is endowment of South Africa with its PGM resources, such as platinum (Pt) and iridium (Ir) that are used in PEM water electrolysis (WE) catalytic components. As it is known, PEMWE technology is very well suited to accommodate intermittency of energy supply associated with renewables. PEMWE technology can also deliver relatively high-pressure hydrogen gas of high purity. South Africa has also superior endowment of both onshore wind and solar. It is known thar renewable energy (RE) is one of the largest operational cost components in the production of green hydrogen. Other factors contributing to the interest in green hydrogen water electrolysis technology in South Africa that are not obvious, but important, include large tracts of sparsely populated land with little alternative use, which can be dedicated for RE production. South Africa also has a suitable geographical position with deep water ports for the potential export of large quantity of hydrogen and its derivatives such as ammonia. Approximately 15 years ago South African Government approved national program HySA: Hydrogen South Africa that resulted in developing expertise and capacity to conduct research, development, and earlier commercial activities around green hydrogen production by means of water electrolysis. These activities include development of local IP at the components, stack and system levels. Recently, a number of “catalytic” projects have been identified in order to increase a demand in green hydrogen and stimulate investments. Recently, an international R&D project between South Africa and Japan was launched to develop further expertise in both green hydrogen and ammonia technologies [1]. Most recently, large companies, such as SASOL, made commitments to lead green hydrogen production at a large scale for the variety of applications, aiming at decarbonisation of mining and petrochemical sectors [2]. On the Governmental level, South Africa recently has approved its national hydrogen road map [3]. This talk will provide a comprehensive update on the research, technology, and commercialisation activities in South Africa in the area of green hydrogen production.

This paper describes a numerical study of the influence of thermal diffusion (the Soret effect) on the operational behaviour of a passive autocatalytic recombiner (PAR). The study pro-poses a detailed three-dimensional computational fluid dynamics (CFD) model of hydrogen oxidation along a cylindrical-type PAR catalyst section (RVK-500, RET, Russia) inside a small-scale vertical channel. The CFD model was developed in STAR-CCM+ and uses multi-step chemical kinetics with a conjugated approach (surface and gas-phase included). The cata-lyst temperature and hydrogen conversion with and without the Soret effect in the model were determined numerically and compared against experimental measurements. The ex-periments reported here have previously been conducted on the cylindrical-type catalyst section, for 5-7 vol % inlet H2 concentration. Numerical simulations demonstrate that local hydrogen concentration can be increased due to thermal diffusion at the lower side of the stainless-steel frame. Results identified that the catalyst temperature can be underpredicted by 10-20 degrees C without thermal diffusion included in the model.(c) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Hydrogen production from renewable energy sources has the potential to significantly reduce the carbon footprint of critical economic sectors that rely heavily on fossil fuels. Liquid organic hydrogen carrier (LOHC) technology has the capability to overcome the limitations associated with conventional hydrogen storage technologies. To date, dibenzyltoluene and benzyltoluene are the benchmark LOHC molecules due to the unique hydrogen storage properties. However, the reaction temperature for dehydrogenation reaction is high and catalysts need to be further developed so that efficient release of hydrogen can be realized. Exploration of various catalyst preparation methods such as supercritical carbon-dioxide deposition, the selection on support material with relevant textural and chemical properties and optimization of catalyst modifiers are rewarding approaches of improving the catalyst performance. In addition to this, the lowering of the dehydrogenation temperature by employing electrochemical methods and reactive distillation approaches are strategies that will make the LOHC technology competitive.

We are proposing a conceptual membrane electrode assembly (MEA) of a proton exchange membrane water electrolyzer that includes a layer of graphene oxide (GO) at the cathode side. This GO layer primarily reinforces the MEA to allow operation at a higher pressure difference between the cathode and anode side. Additional benefits would be that a perfect GO layer would prevent both water and hydrogen crossover and thus would allow for pure, dry hydrogen escaping directly from the electrolyzer without losses due to hydrogen crossover, thus eliminating the need for hydrogen clean-up steps. The mechanical strength of graphene will also allow for a thinner polymer electrolyte membrane and could thus save cost. Finally, the effect of electro–osmotic drag on the water content in such an MEA is discussed, and it is argued that it could lead to an oversaturated membrane, which is highly desirable.

To address the growing demands for renewable energy storage and reduce carbon emissions to the environment, the search for safe and valuable energy storage systems is needed. The environment and human health are unaffected by using hydrogen as a fuel because it is clean, efficient, and environmentally benign. However, the absence of efficient hydrogen storage methods is one of the technical barriers to introducing hydrogen energy on a wider scale. Liquid organic hydrogen carriers (LOHCs) have been viewed as promising potential candidates for hydrogen storage because of their low cost, high hydrogen storage capacity, reversibility, and compatibility with existing energy supply infrastructures. However, associated with LOHCs, there are significant kinetic barriers in the reversible hydrogenation/dehydrogenation processes, which demands the use of effective catalysts. In this review, first-principles studies are given attention in recent activities in advancing the design of heterogeneous catalysts for the dehydrogenation of LOHC compounds—here, the designs include the use of supported catalysts and bimetallic catalysts—and determining the effect of the metal surface (facet dependence) on the mechanism of catalytic activity. The review concludes with a mention of some challenges, and outlook research directions for improved catalyst design in the dehydrogenation of LOHCs.

Low-cost anion exchange membrane (AEM) water electrolysis is a promising technology for producing “green” high-purity hydrogen using platinum group metal (PGM)-free catalysts. The performance of AEM electrolysis depends on the overall overvoltage, e.g., voltage losses coming from different processes in the water electrolyzer including hydrogen and oxygen evolution, non-faradaic charge transfer resistance, mass transfer limitations, and others. Due to the different relaxation times of these processes, it is possible to unravel them in the frequency domain by electrochemical impedance spectroscopy. This study relates to solving and quantifying contributions to the total polarization resistance of the AEM water electrolyzer, including ohmic and charge transfer resistances in the kinetically controlled mode. The high-frequency contribution is proposed to have non-faradaic nature, and its conceivable nature and mechanism are discussed. The characteristic frequencies of unraveled contributions are provided to be used as benchmark data for commercially available membranes and electrodes.

This paper presents the concept of a passive electrochemical hydrogen recombiner (PEHR). The reaction energy of the recombination of hydrogen and oxygen is used as a source of electrical energy according to the operating principle for hydrogen fuel cells to establish forced circulation of the hydrogen mixture as an alternative to natural circulation (as is not utilized in conventional passive autocatalytic hydrogen recombiners currently used in nuclear power plants (NPPs)). The proposed concept of applying the physical operation principles of a PEHR based on a fuel cell simultaneously increases both productivity in terms of recombined hydrogen and the concentration threshold of flameless operation (the ‘ignition’ limit). Thus, it is possible to reliably ensure the hydrogen explosion safety of NPPs under all conditions, including beyond-design accidents. An experimental setup was assembled to test a laboratory sample of a membrane electrode assembly (MEA) at various hydrogen concentrations near the catalytic surfaces of the electrodes, and the corresponding current–voltage characteristics were recorded. The simplest MEA based on the Advent P1100W PBI membrane demonstrated stable performance (delivery of electrical power) over a wide range of hydrogen concentrations.

Alloys are beneficial in numerous applications since they combine the desirable properties of different metals. In this regard, Pt/Pd alloys have been investigated as a replacement for Pt, which is the standard catalyst used in various catalytic processes. However, there are still gaps in our understanding of the structural, mechanical, and thermodynamic properties of Pt/Pd alloys. This study was conducted using density functional theory (DFT) calculations to investigate the electronic, elasticity, mechanical, and thermodynamic properties of Pt/Pd alloys and compared them to pristine Pt and Pd structures. The results indicate that the considered Pt/Pd alloy structures, PtPd3, PtPd, Pt3Pd, and Pt7Pd, are energetically favourable based on their formation energies. These structures also satisfy Born's stability criteria and are elastically stable. The phonon density of states showed that the considered Pt/Pd alloy structures are dynamically stable, with no imaginary modes present. Additionally, the Pt atom dominates at lower frequencies, while the Pd atom dominates at higher frequencies, as seen in the phonon band structure. The electronic density of states revealed that the considered Pt/Pd alloy structures have a metallic character and are non-magnetic. These findings contribute to a better understanding of the properties and stability of Pt/Pd alloy structures that are relevant in various fields, including materials science and catalysis.

Density functional theory (DFT) calculations were used to investigate the surface performance of Pt, Ni, Co, and PtxTM1-x (0 < x < 1) alloys, as well as reaction intermediates (O, H, OH, OH + H, H2O) on these surfaces for H2/ O2 recombination. The activity of the PtxTM1-x alloys towards H2/O2 recombination reaction was probed using adsorption energies and reaction energies. The Pt3Co, Pt3Ni and PtNi3 alloys were found to be stable along the (111) miller index, with strong surface adsorption occurring on the PtNi3 (111) surface and weaker adsorption on the Pt3Co (111) surface. Enhanced reactivity was observed on the Pt3Ni and Pt3Co (111) surfaces for the (O* + H*-* OH*) reaction step, while the Pt (111) surface was most suited for the (OH* + H*-* H2O) reaction step. The OH* formation reaction step was inhibited on the PtNi3 (111) surface due to the strong surface absorption of the reaction intermediates. Overall, these results suggest that the Pt3Co (111) surface is a promising alternative catalyst for H2/O2 recombination compared to pristine Pt due to its performance in the O + H adsorption and OH* formation steps.