Reversible, carbon dioxide mediated chemical hydrogen storage was first demonstrated using a heterogeneous Pd catalyst supported on mesoporous graphitic carbon nitride (Pd/mpg-C₃N₄). The Pd nanoparticles were found to be uniformly dispersed onto mpg-C₃N₄ with an average size of 1.7 nm without any agglomeration and further exhibit superior activity for the dehydrogenation of formic acid with a turnover frequency of 144 h⁻¹ even in the absence of external bases at room temperature. Initial DFT studies suggest that basic sites located at the mpg-C₃N₄ support play synergetic roles in stabilizing reduced Pd nanoparticles without any surfactant as well as in initiating H₂-release by deprotonation of formic acid, and these potential interactions were further confirmed by X-ray absorption near edge structure (XANES). Along with dehydrogenation, Pd/mpg-C₃N₄ also proves to catalyze the regeneration of formic acid via CO₂ hydrogenation. The governing factors of CO₂ hydrogenation are further elucidated to increase the quantity of the desired formic acid with high selectivity.

The success of the so-called “hydrogen economy” for large-scale applications will ultimately depend on efficient and sustainable production, storage and distribution of hydrogen. Owing to its low toxicity, high volumetric H₂ storage capacity and availability both from renewable resources (e.g., biomass) and non-renewable resources (e.g., fossil fuel feedstocks), formic acid is one of the most favorable chemical hydrogen storage media for large-scale energy storage applications. However, for FA to become a viable hydrogen storage medium, efficient catalysts that enable it to release H₂ at low cost are necessary. Herein we report a facile synthetic route to amine-functionalized nanoporous silica-supported ultrasmall Pd nanoparticles (SBA-15-Amine/Pd) that are highly active catalysts for formic acid dehydrogenation, producing hydrogen at ambient temperature with a high turn-over-frequency (TOF) of 293 h⁻¹, which is among the highest TOFs ever reported for the reaction by a heterogeneous catalyst. We also show that the material is easily recyclable multiple times, without losing its catalytic activity. So, the catalyst we developed can be expected to be part of the solutions of our sustainability challenges.

Exfoliated graphitic carbon nitride nanosheets (g-C₃N₄-NS) were applied for the first time for the preparation of an electrocatalyst for the oxygen reduction reaction (ORR). A less dense structure with increased surface area was observed for g-C₃N₄-NS compared to bulk g-C₃N₄ from detailed analyses including TEM, STEM, AFM with depth profiling, XRD, and UV-Vis spectroscopy. The pyrolysis of the prepared g-C₃N₄-NS with Co and carbon under an inert environment provided an enhanced accessibility to the N functionalities required for efficient interaction of Co and C with N for the formation of Co–N–C networks and produced a hollow and interconnected Co–N–C–NS structure responsible for high durability. The Co–N–C–NS electrocatalyst exhibited superior catalytic activity and durability and further displayed fast and selective four electron transfer kinetics for the ORR, as evidenced by various electrochemical experiments. The hollow, interconnected structure of Co–N–C–NS with increased pyridinic and graphitic N species has been proposed to play a key role in facilitating the desired ORR reaction.