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Graphene‐like materials are of interest for large‐scale hydrogen storage applications due to their lightweight, durable, and scalable properties. Nitrogen‐doping minimizes kinetic limitations in diffusion and recombination on surfaces, however, the role of graphitic nitrogen (GN) and pyridinic nitrogen (PN) is not well understood. Nitrogen‐doped graphene is synthesized on Ru(0001) using chemical vapor deposition (CVD) of pyridine and ion irradiation. Scanning tunneling microscopy (STM), x‐ray photoelectron spectroscopy (XPS), and density functional theory (DFT) are used to identify the structure, location, and thermodynamic stability of nitrogen species within the graphene moiré. CVD of pyridine results in a low nitrogen concentration (<0.1at%), while the post‐growth nitrogen ion irradiation allows us to increase the concentration further. The concentration of GN and PN is controlled by varying the ion dose and annealing temperature. Comparison of measured and simulated STM images of GN and PN yield an excellent agreement, allowing us to confidently establish that GN is preferentially located near the center of the Atop region, while PN is located in the valley region of the graphene moiré. This report explicitly confirms the site assignments and provides a foundation for the site synthesis and analysis of structural and electronic properties that drive the reactivity of N‐doped graphene. Nitrogen doping on Ru(0001) is investigated using ion implantation and annealing, tuning the distribution of graphitic (GN) and pyridinic (PN) nitrogen sites. STM, XPS, and DFT identified the structure and site distribution, and a thermodynamic phase diagram showed that GN is most stable at the Atop region, while PN preferred boundaries between FCC and HCP regions of the graphene moiré.

We examined the effects of concentrations and identities of various glymes, from monoglyme up to tetraglyme, on H2 release from the thermolysis of Mg(BH4)2 at 160–200 °C for 8 h. 11B NMR analysis shows major products of Mg(B10H10) and Mg(B12H12); however, their relative ratio is highly dependent both on the identity and concentration of the glyme to Mg(BH4)2. Selective formation of Mg(B10H10) was observed with an equivalent of monoglyme and 0.25 equivalent of tetraglyme. However, thermolysis of Mg(BH4)2 in the presence of stoichiometric or greater equivalent of glymes can lead to unselective formation of Mg(B10H10) and Mg(B12H12) products or inhibition of H2 release.

Tetrahydofuran (THF) complexed to magnesium borohydride has been found to have a positive effect on both the reactivity and selectivity, enabling release of H2 at <200 °C and forms Mg(B10H10) with high selectivity.

Hydrogen has the highest gravimetric energy density of any energy carrier and produces water as the only oxidation product, making it extremely attractive for both transportation and stationary power applications. However, its low volumetric energy density causes considerable difficulties, inspiring intense efforts to develop chemical-based storage using metal hydrides, liquid organic hydrogen carriers and sorbents. The controlled uptake and release of hydrogen by these materials can be described as a series of challenges: optimal properties fall within a narrow range, can only be found in few materials and often involve important trade-offs. In addition, a greater understanding of the complex kinetics, mass transport and microstructural phenomena associated with hydrogen uptake and release is needed. The goal of this Perspective is to delineate potential use cases, define key challenges and show that solutions will involve a nexus of several subdisciplines of chemistry, including catalysis, data science, nanoscience, interfacial phenomena and dynamic or phase-change materials. Hydrogen, which possesses the highest gravimetric energy density of any energy carrier, is attractive for both mobile and stationary power, but its low volumetric energy density poses major storage and transport challenges. This Perspective delineates potential use cases and defines the challenges facing the development of materials for efficient hydrogen storage.

A Liquid Organic Hydrogen Carrier (LOHC) enables the storage and transport of hydrogen at ambient pressures and temperatures in a safe and convenient form using current infrastructure. However, it is challenging to directly compare reactivity and selectivity for hydrogen release, especially when comparing the catalytic efficiencies of neat LOHCs to highly diluted LOHCs in different solvents, reaction conditions, and catalysts. This work evaluates the role of solvents in catalysis and quantifies the energy efficiency of the overall process. The presence of solvent dilutes the volumetric density of available hydrogen, but may be necessary to achieve optimal catalysts stability, reactivity, and product selectivity. With respect to the reaction conditions as determined by thermodynamics, solvents with higher vapor pressures than that of the carrier can cause the erroneous impression of a more favorable reaction equilibrium. Concerning energy efficiency, solvents can result in increased energy demand for hydrogen release as the inert solvent must be heated to reaction temperatures required for release of H 2 from the LOHC. This work recommends that investigations of catalyst reactivity should be carried out at different ratios of solvent to LOHC to understand how the reactivity changes and what the implications are for maximizing energy density and catalyst stability and reactivity. Investigations should also consider how these implications will affect the technical needs of applications intended for the LOHC system. Based on the results of this study, it is advised to focus research activities on LOHC systems with a gravimetric solvent content below about 50% as the thermodynamic disadvantages become very pronounced beyond this threshold.

Hydrogen offers a route to storing renewable electricity and lowering greenhouse gas emissions. Metal–organic framework (MOF) adsorbents are promising candidates for hydrogen storage, but a deep understanding of their potential for large-scale, stationary back-up power applications has been lacking. Here we utilize techno-economic analysis and process modelling, which leverage molecular simulation and experimental results, to evaluate the future opportunities of MOF-stored hydrogen for back-up power applications and set critical targets for future material development. We show that with carefully designed charging–discharging patterns, MOFs coupled with electrolysers and fuel cells are economically comparable with contemporary incumbent energy-storage technologies in back-up power applications. Future research should target developing MOFs with 15 g kg −1 of recoverable hydrogen adsorbed (excess uptake) and could be manufactured for under US$10 kg −1 to make the on-site storage system a leading option for back-up power applications. Metal–organic frameworks (MOFs) are promising candidates to store hydrogen for transportation, but less focus has been on their potential for storage in large-scale, stationary applications. Here Peng et al. perform techno-economic analysis and process modelling to evaluate the prospects of MOFs for back-up power.

Electrification to reduce or eliminate greenhouse gas emissions is essential to mitigate climate change. However, a substantial portion of our manufacturing and transportation infrastructure will be difficult to electrify and/or will continue to use carbon as a key component, including areas in aviation, heavy-duty and marine transportation, and the chemical industry. In this Roadmap, we explore how multidisciplinary approaches will enable us to close the carbon cycle and create a circular economy by defossilizing these difficult-to-electrify areas and those that will continue to need carbon. We discuss two approaches for this: developing carbon alternatives and improving our ability to reuse carbon, enabled by separations. Furthermore, we posit that co-design and use-driven fundamental science are essential to reach aggressive greenhouse gas reduction targets. To achieve net-zero carbon emissions, we must close the carbon cycle for industries that are difficult to electrify. Developing the needed science to provide carbon alternatives and non-fossil carbon will accelerate advances towards defossilization.

We have examined the chemical and physical properties of two acylnitrenes, 4-acetylphenoxycarbonylnitrene (APN) and $\\beta$-naphthoylnitrene (BNN) generated by the photolysis of 4-acetylphenoxycarbonyl azide and $\\beta$-naphthoyl azide (BNA) respectively. These nitrenes were investigated using low-temperature optical, electron spin resonance, and transient absorption spectroscopy as well as by traditional chemical trapping techniques. APN is a ground state triplet nitrene which appears to be no more than 5 kcal/mol below the lowest energy singlet nitrene. The properties of APN are dominated by those typically associated with triplet nitrenes: nonstereospecific addition to olefins and a readily detectable electron spin resonance spectrum. BNN is the first bona fide example of an acylnitrene with a singlet ground state. The properties of BNN are those typically associated with singlet nitrenes: direct or triplet sensitized irradiation of BNA gives products derived exclusively from the singlet nitrene.