France

Delayed explosion of free field hydrogen releases at a high pressure is subject of multiple investigation performed by various authors in the past years. These studied considered various parameters such as pressures flow rates etc. and their influence on the resulting overpressure. However the influence of the ignition position on the maximum overpressure was not fully explored. Current investigation addressed by computational fluid dynamics (CFD) simulations and experimental measurement fills this gap. This work demonstrates that the ignition positions corresponding to 55%-65% of H2/air mixture give the maximum overpressure. This observation initially observed numerically and afterword confirmed experimentally. A simple model is also suggested.

Nanoporous carbons remain the most promising candidates for effective hydrogen storage by physisorption in currently foreseen hydrogen-based scenarios of the world’s energy future. An optimal sorbent meeting the current technological requirement has not been developed yet. Here we first review the storage limitations of currently available nanoporous carbons then we discuss possible ways to improve their storage performance. We focus on two fundamental parameters determining the storage (the surface accessible for adsorption and hydrogen adsorption energy). We define numerically the values nanoporous carbons have to show to satisfy mobile application requirements at pressures lower than 120 bar. Possible necessary modifications of the topology and chemical compositions of carbon nanostructures are proposed and discussed. We indicate that pore wall fragmentation (nano-size graphene scaffolds) is a partial solution only and chemical modifications of the carbon pore walls are required. The positive effects (and their limits) of the carbon substitutions by B and Be atoms are described. The experimental ‘proof of concept’ of the proposed strategies is also presented. We show that boron substituted nanoporous carbons prepared by a simple arc-discharge technique show a hydrogen adsorption energy twice as high as their pure carbon analogs. These preliminary results justify the continuation of the joint experimental and numerical research effort in this field.

Mass-produced off-the-shelf automotive air compressors cannot be directly used for boosting a fuel cell vehicle (FCV) application in the same way that they are used in internal combustion engines since the requirements are different. These include a high pressure ratio a low mass flow rate a high efficiency requirement and a compact size. From the established fuel cell types the most promising for application in passenger cars or light commercial vehicle applications is the proton exchange membrane fuel cell (PEMFC) operating at around 80 ◦C. In this case an electric-assisted turbocharger (E-turbocharger) and electric supercharger (single or two-stage) are more suitable than screw and scroll compressors. In order to determine which type of these boosting options is the most suitable for FCV application and assess their individual merits a co-simulation of FCV powertrains between GT-SUITE and MATLAB/SIMULINK is realised to compare vehicle performance on the Worldwide Harmonised Light Vehicle Test Procedure (WLTP) driving cycle. The results showed that the vehicle equipped with an E-turbocharger had higher performance than the vehicle equipped with a two-stage compressor in the aspects of electric system efficiency (+1.6%) and driving range (+3.7%); however for the same maximal output power the vehicle’s stack was 12.5% heavier and larger. Then due to the existence of the turbine the E-turbocharger led to higher performance than the single-stage compressor for the same stack size. The solid oxide fuel cell is also promising for transportation application especially for a use as range extender. The results show that a 24-kWh electric vehicle can increase its driving range by 252% due to a 5 kW solid oxide fuel cell (SOFC) stack and a gas turbine recovery system. The WLTP driving range depends on the charge cycle but with a pure hydrogen tank of 6.2 kg the vehicle can reach more than 600 km.

The need to reduce CO2 emissions to zero by 2050 has meant an increasing focus on high emitting industrial sectors such as steel. However significant uncertainties remain as to the rate of technology diffusion across steel production pathways in different regions and how this might impact on climate ambition. Informed by empirical analysis of historical transitions this paper presents modelling on the regional deployment of Direction Reduction Iron using hydrogen (DRI-H2). We find that DRI-H2 can play a leading role in the decarbonisation of the sector leading to near-zero emissions by 2070. Regional spillovers from early to late adopting regions can speed up the rate of deployment of DRI-H2 leading to lower cumulative emissions and system costs. Without such effects cumulative emissions are 13% higher than if spillovers are assumed and approximately 15% and 20% higher in China and India respectively. Given the estimates of DRI-H2 cost-effectiveness relative to other primary production technologies we also find that costs increase in the absence of regional spillovers. However other factors can also have impacts on deployment emission reductions and costs including the composition of the early adopter group material efficiency improvements and scrap recycling rates. For the sector to achieve decarbonisation key regions will need to continue to invest in low carbon steel projects recognising their broader global benefit and look to develop and strengthen policy coordination on technologies such as DRI-H2.

A Lagrangian-based one-dimensional approach has been developed using Cantera to study the dynamics of spherically expanding flames. The detailed reaction model USC-Mech II has been employed to examine flame propagating in hydrogen-air mixtures. In the first part our approach has been validated against laminar flame speed and Markstein number data from the literature. It was shown that the laminar flame speed was predicted within 5% on average but that discrepancies were observed for the Markstein number especially for rich mixtures. In the second part a detailed analysis of the thermo-chemical dynamics along the path of Lagrangian particles propagating in stretched flames was performed. For mixtures with negative Markstein lengths it was found that at high stretch rates the mixture entering the reaction-dominated period is less lean with respect to the initial mixture than at low stretch rate. This induces a faster rate of chemical heat release and of active radical production which results in a higher flame propagation speed. Opposite effects were observed for mixtures with positive Markstein lengths for which slower flame propagation was observed at high stretch rates compared to low stretch rates."

With the clear adverse impacts of fossil fuel-based energy systems on the climate and environment ever-growing interest and rapid developments are taking place toward full or nearly full dependence on renewable energies in the next few decades. Estonia is a European country with large demands for electricity and thermal energy for district heating. Considering it as the case study this work explores the feasibility and full potential of optimally sized photovoltaic (PV) wind and PV/wind systems equipped with electric and thermal storage to fulfill those demands. Given the large excess energy from 100% renewable energy systems for an entire country this excess is utilized to first meet the district heating demand and then to produce hydrogen fuel. Using simplified models for PV and wind systems and considering polymer electrolyte membrane (PEM) electrolysis a genetic optimizer is employed for scanning Estonia for optimal installation sites of the three systems that maximize the fulfillment of the demand and the supply–demand matching while minimizing the cost of energy. The results demonstrate the feasibility of all systems fully covering the two demands while making a profit compared to selling the excess produced electricity directly. However the PV-driven system showed enormous required system capacity and amounts of excess energy with the limited solar resources in Estonia. The wind system showed relatively closer characteristics to the hybrid system but required a higher storage capacity by 75.77%. The hybrid PV/wind-driven system required a total capacity of 194 GW most of which belong to the wind system. It was also superior concerning the amount (15.05 × 109 tons) and cost (1.42 USD/kg) of the produced green hydrogen. With such full mapping of the installation capacities and techno-economic parameters of the three systems across the country this study can assist policymakers when planning different country-scale cogeneration systems.

The present work is concerned with the evaluation of the tightness of the components located on domestic and commercial gas lines from the gas meter to the end user appliance in presence of a mixture 40%H2+60%CH4 at 35 mbar. The components were taken from installations being used currently in Germany Denmark Belgium and France. The current standard methods to evaluate natural gas distribution tightness propose testing duration of several minutes. In this work the components tightness was first evaluated using such standard methods before carrying out tests on longer period of time and evaluate the potential influence of time and the results were compared to admissible leakage rates for natural gas in distribution network and in appliances.

In this paper we implement a long-term multi-sectoral energy planning model to evaluate the role of green hydrogen in the energy mix of Chile a country with a high renewable potential under stringent emission reduction objectives in 2050. Our results show that green hydrogen is a cost-effective and environmentally friendly route especially for hard-to-abate sectors such as interprovincial and freight transport. They also suggest a strong synergy of hydrogen with electricity generation from renewable sources. Our numerical simulations show that Chile should (i) start immediately to develop hydrogen production through electrolyzers all along the country (ii) keep investing in wind and solar generation capacities ensuring a low cost hydrogen production and reinforce the power transmission grid to allow nodal hydrogen production (iii) foster the use of electric mobility for cars and local buses and of hydrogen for long-haul trucks and interprovincial buses and (iv) develop seasonal hydrogen storage and hydrogen cells to be exploited for electricity supply especially for the most stringent emission reduction objectives.

Underground Hydrogen storage (UHS) is a promising technology for safe storage of large quantities of hydrogen in daily to seasonal cycles depending on the consumption requirements. The development of UHS requires anticipating hydrogen behavior to prevent any unexpected economic or environmental impact. An open question is the hydrogen reactivity in underground porous media storages. Indeed there is no consensus on the effects or lack of geochemical reactions in UHS operations because of the strong coupling with the activity of microbes using hydrogen as electron donor during anaerobic reduction reactions. In this work we apply different geochemical models to abiotic conditions or including the catalytic effect of bacterial activity in methanogenesis acetogenesis and sulfate-reduction reactions. The models are applied to Lobodice town gas storage (Czech Republic) where a conversion of hydrogen to methane was measured during seasonal gas storage. Under abiotic conditions no reaction is simulated. When the classical thermodynamic approach for aqueous redox reactions is applied the simulated reactivity of hydrogen is too high. The proper way to simulate hydrogen reactivity must include a description of the kinetics of the aqueous redox reactions. Two models are applied to simulate the reactions of hydrogen observed at Lobodice gas storage. One modeling the microbial activity by applying energy threshold limitations and another where microbial activity follows a Monod-type rate law. After successfully calibrating the bio-geochemical models for hydrogen reactivity on existing gas storage data and constraining the conditions where microbial activity will inhibit or enhance hydrogen reactivity we now have a higher confidence in assessing the hydrogen reactivity in future UHS in aquifers or depleted reservoirs.

Methane pyrolysis is a transitional technology for environmentally benign hydrogen production with zero greenhouse gas emissions especially when concentrated solar energy is the heating source for supplying high-temperature process heat. This study is focused on solar methane pyrolysis as an attractive decarbonization process to produce both hydrogen gas and solid carbon with zero CO2 emissions. Direct normal irradiance (DNI) variations arising from inherent solar resource variability (clouds fog day-night cycle etc.) generally hinder continuity and stability of the solar process. Therefore a novel hybrid solar/electric reactor was designed at PROMES-CNRS laboratory to cope with DNI variations. Such a design features electric heating when the DNI is low and can potentially boost the thermochemical performance of the process when coupled solar/electric heating is applied thanks to an enlarged heated zone. Computational fluid dynamics (CFD) simulations through ANSYS Fluent were performed to investigate the performance of this reactor under different operating conditions. More particularly the influence of various process parameters including temperature gas residence time methane dilution and hybridization on the methane conversion was assessed. The model combined fluid flow hydrodynamics and heat and mass transfer coupled with gas-phase pyrolysis reactions. Increasing the heating temperature was found to boost methane conversion (91% at 1473 K against ~100% at 1573 K for a coupled solar-electric heating). The increase of inlet gas flow rate Q0 lowered methane conversion since it affected the gas space-time (91% at Q0 = 0.42 NL/min vs. 67% at Q0 = 0.84 NL/min). A coupled heating also resulted in significantly better performance than with only electric heating because it broadened the hot zone (91% vs. 75% methane conversion for coupled heating and only electric heating respectively). The model was further validated with experimental results of methane pyrolysis. This study demonstrates the potential of the hybrid reactor for solar-driven methane pyrolysis as a promising route toward clean hydrogen and carbon production and further highlights the role of key parameters to improve the process performance.

Governments and local authorities introduce new incentives and regulations for cleaner mobility as part of their environmental strategies to address energy challenges. Fuel cell electric vehicles (FCEVs) are becoming increasingly important and will extend beyond captive fleets reaching private users. Research on hydrogen safety issues is currently led in several projects in order to highlight and manage risks of FCEVs in confined spaces such as tunnels underground parkings repair garages etc. But what about private garages - that involve specific geometries volumes congestion ventilation? This study has been carried out in the framework of PRHyVATE JIP project which aims at better understanding hydrogen build-up and distribution in a private garage. The investigation went through different rates and modes of ventilation. As first step an HAZID (Hazard Identification) has been realized for a generic FCEV. This preliminary work allowed to select and prioritize accidental release scenarios to be explored experimentally with helium in a 40-m3 garage. Several configurations of release ventilation modes and congestion – in transient regime and at steady state – have been tested. Then analytical and numerical calculation approaches have been applied and adjusted to develop a simplified methodology. This methodology takes into account natural ventilation for assessment of hydrogen accumulation and mitigation means optimization. Finally a global risk evaluation – including ignition of a flammable hydrogen-air mixture – has been performed to account for the mostly feared events and to evaluate their consequences in a private garage. Thus preliminary recommendations good practices and safety features for safely parking FCEVs in private garages can be proposed.

The use of hydrogen as energy carrier in a low emission microturbine could be an interesting option for renewable energy storage distributed generation and combined heat & power. However the hydrogen using in gas turbine is limited by the NOx emissions and the difficulty to operate safely. CFD simulations represent a powerful and mature tool to perform detailed 3-D investigation for the development of a prototype before carrying out an experimental analysis. This paper describes the CFD supported redesign of the Turbec T100 microturbine combustion chamber natural gas-fired to allow the operation on 100% hydrogen.

The main objective of the article is to provide a thorough review of currently used AC-DC converters for alkaline and proton exchange membrane (PEM) electrolyzers in power grid or wind energy conversion systems. Based on the current literature this article aims at emphasizing the advantages and drawbacks of AC-DC converters mainly based on thyristor rectifier bridges and chopper-rectifiers. The analysis is mainly focused on the current issues for these converters in terms of specific energy consumption current ripple reliability efficiency and power quality. From this analysis it is shown that thyristors-based rectifiers are particularly fit for high-power applications but require the use of active and passive filters to enhance the power quality. By comparison the association combination of the chopper-rectifier can avoid the use of bulky active and passive filters since it can improve power quality. However the use of a basic chopper (i.e. buck converter) presents several disadvantages from the reliability energy efficiency voltage ratio and current ripple point of view. For this reason new emerging DC-DC converters must be employed to meet these important issues according to the availability of new power switching devices. Finally based on the authors’ experience in power conversion for PEM electrolyzers a discussion is provided regarding the future challenges that must face power electronics for green hydrogen production based on renewable energy sources.

The highly combustible nature of hydrogen poses a great hazard creating a number of problems with its safety and handling. As a part of safety studies related to the use of hydrogen in a confined environment it is extremely important to have a good knowledge of the dispersion mechanism.<br/>The present work investigates the concentration field and flammability envelope from a small scale leak. The hydrogen is released into a 0.47 m × 0.33 m x 0.20 m enclosure designed as a 1/15 – scale model of a room in a nuclear facility. The performed tests evaluates the influence of the initial conditions at the leakage source on the dispersion and mixing characteristics in a confined environment. The role of the leak location and the presence of obstacles are also analyzed. Throughout the test during the release and the subsequent dispersion phase temporal profiles of hydrogen concentration are measured using thermal conductivity gauges within the enclosure. In addition the BOS (Background Oriented Schlieren) technique is used to visualise the cloud evolution inside the enclosure. These instruments allow the observation and quantification of the stratification effects.

Buffers are key components for hydrogen filling stations that are currently being developed. Type 1 or composite cylinders are used for this application. The type used depends on many parameters including pressure level cost and space available for the filling station. No international standards exist for such high pressure vessels whereas many standards exist covering Types 123 and 4 used for transport of gas or on-board fuel tanks. It is suggested to use the cylinders approved for transport or on-board applications as buffers. This solution appears to be safe if at least one issue is solved. The main difference is that transport or on-board cylinders are cycled from a low pressure to a high pressure during service whereas buffers are cycled from a relatively high pressure (corresponding to the vehicle’s filling pressure) to the MAWP. Another difference is that buffers are cycled many times per day. For standards developers requesting to systematically verify that buffers pass millions of cycles at low pressure amplitude would be impractical. Several standards and codes give formulae to estimate the number of shallow cycles when number of deep cycles are known. In this paper we describe tests performed on all types of composite cylinders to verify or determine the appropriate formulae.

Liquid hydrogen (LH2) compared to compressed gaseous hydrogen offers advantages for large-scale transport and storage of hydrogen with higher densities. Although the gas industry has good experience with LH2 only little experience is available for the new applications of LH2 as an energy carrier. Therefore the European FCH JU funded project PRESLHY conducted pre-normative research for the safe use of cryogenic LH2 in non-industrial settings. The central research consisted of a broad experimental program combined with analytical work modelling and simulations belonging to the three key phenomena of the accident chain: release and mixing ignition and combustion. The presented results improve the general understanding of the behavior of LH2 in accidents and provide some design guidelines and engineering tools for safer use of LH2. Recommendations for improvement of current international standards are derived.

We have designed a new method for electrochemical hydrogen charging which allows us to charge very thin coarse-grained specimens from the bottom and perform nanomechanical testing on the top. As the average grain diameter is larger than the thickness of the sample this setup allows us to efficiently evaluate the mechanical properties of multiple single crystals with similar electrochemical conditions. Another important advantage is that the top surface is not affected by corrosion by the electrolyte. The nanoindentation results show that hydrogen reduces the activation energy for homogenous dislocation nucleation by approximately 15–20% in a (001) grain. The elastic modulus also was observed to be reduced by the same amount. The hardness increased by approximately 4% as determined by load-displacement curves and residual imprint analysis.

Although hydrogen is considered to be one of the most promising green fuels its efficient and safe storage and use still raise several technological challenges. Physisorption in porous materials may offer an attractive means of  storage but the state-of-the-art capacity of these kinds of systems is still limited. To overcome the present drawbacks a deeper understanding of the adsorption and surface diffusion mechanism is required along with new types of adsorbents developed and/or optimised for this purpose. In the present study we compare the hydrogen adsorption behaviour of three carbon gels exhibiting different porosity and/or surface chemistry. In addition to standard adsorption characterisation techniques neutron spin-echo spectroscopy (NSE) has been also applied to explore the surface mobility of the adsorbed hydrogen. Our results reveal that both the porosity and surface chemistry of the adsorbent play a significant role in the adsorption of  in these systems.

Diesel generators are currently used as an off-grid solution for backup power but this causes CO2 and GHG emissions noise emissions and the negative effects of the volatile diesel market influencing operating costs. Green hydrogen production by means of water electrolysis has been proposed as a feasible solution to fill the gaps between demand and production the main handicaps of using exclusively renewable energy in isolated applications. This manuscript presents a business case of an off-grid hydrogen production by electrolysis applied to the electrification of isolated sites. This study is part of the European Ely4off project (n◦ 700359). Under certain techno-economic hypothesis four different system configurations supplied exclusively by photovoltaic are compared to find the optimal Levelized Cost of Electricity (LCoE): photovoltaic-batteries photovoltaic-hydrogen-batteries photovoltaic-diesel generator and diesel generator; the influence of the location and the impact of different consumptions profiles is explored. Several simulations developed through specific modeling software are carried out and discussed. The main finding is that diesel-based systems still allow lower costs than any other solution although hydrogen-based solutions can compete with other technologies under certain conditions.

LCAs of electric cars and electrolytic hydrogen production are governed by the consumption of electricity. Therefore LCA benchmarking is prone to choices on electricity data. There are four issues: (1) leading Life Cycle Impact (LCI) databases suffer from inconvenient uncertainties and inaccuracies (2) electricity mix in countries is rapidly changing year after year (3) the electricity mix is strongly fluctuating on an hourly and daily basis which requires time-based allocation approaches and (4) how to deal with nuclear power in benchmarking. This analysis shows that: (a) the differences of the GHG emissions of the country production mix in leading databases are rather high (30%) (b) in LCA a distinction must be made between bundled and unbundled registered electricity certificates (RECs) and guarantees of origin (GOs); the residual mix should not be applied in LCA because of its huge inaccuracy (c) time-based allocation rules for renewables are required to cope with periods of overproduction (d) benchmarking of electricity is highly affected by the choice of midpoints and/or endpoint systems and (e) there is an urgent need for a new LCI database based on measured emission data continuously kept up-to-date transparent and open access.

The main goal of THyGA’s WP5 is to investigate ways to adapt residential or commercial appliances that have safety or performance issues to different levels of H2 concentrations in natural gas. This first deliverable presents some possible mitigation measures based on a literature study and some calculations.<br/>Acting on gas quality to avoid that hydrogen addition enhance current gas properties variations was explored several times in the past. Designing new appliances that could operate with variable gas composition including hydrogen. Dealing with existing appliances in order to guaranty safety for users and appliances.

The thermochemical conversion of methane (CH4) and water (H2O) to syngas and hydrogen via chemical looping using concentrated sunlight as a sustainable source of process heat attracts considerable attention. It is likewise a means of storing intermittent solar energy into chemical fuels. In this study solar chemical looping reforming of CH4 and H2O splitting over non-stoichiometric ceria (CeO2/CeO2−δ) redox cycle were experimentally investigated in a volumetric solar reactor prototype. The cycle consists of (i) the endothermic partial oxidation of CH4 and the simultaneous reduction of ceria and (ii) the subsequent exothermic splitting of H2O and the simultaneous oxidation of the reduced ceria under isothermal operation at ~1000°C enabling the elimination of sensible heat losses as compared to non-isothermal thermochemical cycles. Ceria-based reticulated porous ceramics with different sintering temperatures (1000 and 1400°C) were employed as oxygen carriers and tested with different methane flow rates (0.1–0.4 NL/min) and methane concentrations (50 and 100%). The impacts of operating conditions on the foam-averaged oxygen non-stoichiometry (reduction extent δ) syngas yield methane conversion solar-to-fuel energy conversion efficiency as well as the effects of transient solar conditions were demonstrated and emphasized. As a result clean syngas was successfully produced with H2/CO ratios approaching 2 during the first reduction step while high-purity H2 was subsequently generated during the oxidation step. Increasing methane flow rate and CH4 concentration promoted syngas yields up to 8.51 mmol/gCeO2 and δ up to 0.38 at the expense of enhanced methane cracking reaction and reduced CH4 conversion. Solar-to-fuel energy conversion efficiency namely the ratio of the calorific value of produced syngas to the total energy input (solar power and calorific value of converted methane) and CH4 conversion were achieved in the range of 2.9–5.6% and 40.1–68.5% respectively.

A polyethylene (PE) liner is the basic element in high-pressure type 4 composite vessels designed for hydrogen or compressed natural gas (CNG) storage systems. Liner defects may result in the elimination of the whole vessel from use which is very expensive both at the manufacturing and exploitation stage. The goal is therefore the development of efficient non-destructive testing (NDT) methods to test a liner immediately after its manufacturing before applying a composite reinforcement. It should be noted that the current regulations codes and standards (RC&S) do not specify liner testing methods after manufacturing. It was considered especially important to find a way of locating and assessing the size of air bubbles and inclusions and the field of deformations in liner walls. It was also expected that these methods would be easily applicable to mass-produced liners. The paper proposes the use of three optical methods namely visual inspection digital image correlation (DIC) and optical fiber sensing based on Bragg gratings (FBG). Deformation measurements are validated with finite element analysis (FEA). The tested object was a prototype of a hydrogen liner for high-pressure storage (700 bar). The mentioned optical methods were used to identify defects and measure deformations.

Photoanodes comprising a transparent glass substrate coated with a thin conductive film of fluorine-doped tin oxide (FTO) and a thin layer of a photoactive phase have been fabricated and tested with regard to the photo-electro-oxidation of water into molecular oxygen. The photoactive layer was made of a mat of TiO₂ nanorods (TDNRs) of micrometric thickness. Individual nanorods were successfully photosensitized with nanoparticles of a metal–organic framework (MOF) of nickel and 12-benzene dicarboxylic acid (BDCA). Detailed microstructural information was obtained from SEM and TEM analysis. The chemical composition of the active layer was determined by XRD XPS and FTIR analysis. Optical properties were determined by UV–Vis spectroscopy. The water photooxidation activity was evaluated by linear sweep voltammetry and the robustness was assessed by chrono-amperometry. The OER (oxygen evolution reaction) photo-activity of these photoelectrodes was found to be directly related to the amount of MOF deposited on the TiO₂ nanorods and was therefore maximized by adjusting the MOF content. The microscopic reaction mechanism which controls the photoactivity of these photoelectrodes was analyzed by photo-electrochemical impedance spectroscopy. Microscopic rate parameters are reported. These results contribute to the development and characterization of MOF-sensitized OER photoanodes.

Hydrogen (H₂) shows great promise as zero-carbon emission fuel but there are several challenges to overcome in regards to storage and transportation to make it a more universal energy solution. Gaseous hydrogen requires high pressures and large volume tanks while storage of liquid hydrogen requires cryogenic temperatures; neither option is ideal due to cost and the hazards involved. Storage in the solid state presents an attractive alternative and can meet the U.S. Department of Energy (DOE) constraints to find materials containing > 7 % H₂ (gravimetric weight) with a maximum H₂ release under 125 °C.

While there are many candidate hydrogen storage materials the vast majority are metal hydrides. Of the hydrides this review focuses solely on sodium borohydride (NaBH4) which is often not covered in other hydride reviews. However as it contains 10.6% (by weight) H₂ that can release at 133 ± 3 JK−1mol⁻¹ this inexpensive material has received renewed attention. NaBH4 should decompose to H₂g) Na(s) and B(s) and could be recycled into its original form. Unfortunately metal to ligand charge transfer in NaBH4 induces high thermodynamic stability creating a high decomposition temperature of 530 °C. In an effort make H₂ more accessible at lower temperatures researchers have incorporated additives to destabilize the structure.

This review highlights metal additives that have successfully reduced the decomposition temperature of NaBH₄ with temperatures ranging from 522 °C (titanium (IV) fluoride) to 379 °C (niobium (V) fluoride). We describe synthetic methods employed chemical pathways taken and the challenges of boron derivative formation on H₂ cycling. Though no trends can be found across all additives it is our hope that compiling the data here will enable researchers to gain a better understanding of the additives’ influence and to determine how a new system might be designed to make NaBH4 a more viable H2 fuel source.