We present the design and comprehensive investigation of stable para-substituted triarylamine–2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) radical ion pairs (RIPs) generated via single-electron transfer (SET). We quantified the degree of SET in both solution and solid phases, utilising a suite of spectroscopic techniques including IR, EPR, NMR, and single-crystal X-ray diffraction (SC–XRD). Our findings reveal that the extent of SET is significantly influenced by the nature of the substituents (MeO > tBu > Br) and the polarity of the solvent (MeCN > DCM > toluene). The radical ion pair [(pMeOPh)3N]⋅+[DDQ]⋅− was unambiguously identified using EPR and UV–vis spectroscopy, and its structure was confirmed by SC–XRD. Detailed analysis indicates an open-shell singlet ground state with a thermally accessible triplet state, as corroborated by EPR, magnetic susceptibility measurements, and DFT calculations. This study offers crucial insights into the mechanistic pathways of RIP formation and tuning both in solution and solid states, laying the groundwork for future exploration of their reactivity and potential applications.@en

Green hydrogen combined with PEM fuel cell systems is a viable option to meet the demand for alternative maritime fuels. However, hydrogen storage faces challenges, including low volumetric density, fire and explosion risks and transport challenges. We assessed over fifteen hydrogen carriers based on their maritime performance characteristics to determine their suitability for shipboard use. Evaluation criteria included energy density, locally zero-emission, circularity of process, safety, dehydrogenation process, logistic availability and handling. Thus, excluding ammonia and methanol because of these constraints, we found that borohydrides, liquid organic hydrogen carriers and ammoniaborane are the most promising hydrogen carriers to use on ships with PEM fuel cells. Borohydrides, specifically sodium borohydride, have high energy densities but face regeneration issues. The liquid organic hydrogen carrier dibenzyltoluene has a lower energy density but exhibits easy hydrogenation and good handling. Given varying operational demands, we developed a framework to assess the suitability of hydrogen carriers for use in different ship categories. Evaluating the three types of hydrogen carriers, using our framework and considering current practices, shows that these are viable options for almost all ship types. Thus, we have identified three types of hydrogen carriers, which should be the focus of future research.

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Increasing pressure on the reduction or elimination of the use of fossil fuels in shipping requires the application of new maritime fuel alternatives. Green and circular produced hydrogen as a maritime fuel in fuel cell systems offers a great solution for these concerns. A fuel cell system has a zero emission performance, solid state silent process cycle, graceful degradation and no single point of failure. From a naval perspective, these characteristics very much support operational requirements like a silent propulsion and very low thermal and acoustic signatures as well as the possibility of an air independent system. Storage of hydrogen, however, is an issue. Traditional hydrogen storage in gas or liquefied aggregation has low volumetric density, low flame point, fire and explosion risks and transport challenges. The aim of this literature review is to investigate several hydrogen carriers and evaluate their characteristics on maritime and naval performance. This includes their volumetric and gravimetric density, dehydrogenation process, safety, logistic availability and handling. Over 15 different (types of) hydrogen carriers have been researched. Borohydrides, specifically sodium borohydride appeared to have several advantages, but still has issues with its hydrogenation process and handling due to it being a solid. The liquid organic hydrogen carrier dibenzyl toluene, on the other hand, does not meet the required energy density, but does have favourable additional properties, such as easy hydrogenation and good handling. Both of these are also subject of current research and development: For example, Hydrogenious LOHC Maritime AS, in combination with �stensj? Rederi, is working on a megawatt application for maritime, which should be finished in 2025. The Dutch government funds the SH2IPDRIVE project and the European Interreg North West Europe organization funds the H2SHIPS research project to analyse the shipboard use of these hydrogen carriers and to establish the design and engineering optimization opportunities.@en