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This study demonstrates an all-graphene, additive-free, aqueous-based ink for direct ink writing (DIW) to 3D-print functional aerogels for applications in electronics and electromagnetic interference (EMI) shields. We employ a two-step electrochemical method with a specially designed intercalation step that controls the surface functionality of graphene nanosheets. Comprehensive characterization reveals the significant impact of the physicochemical properties of graphene nanosheets on homogeneity, rheology, electrical conductivity, and EMI shielding effectiveness (SE). A critical observation is that rheology alone is insufficient to predict the printability of two-dimensional particulate systems, while ink homogeneity, dictated by inter-sheet interactions, plays a vital role. By focusing on optimizing intercalation conditions, we find that phosphoric acid treatment is most effective in enhancing both printability and conductivity, achieving an electrical conductivity of 158 S cm−1 and an EMI SE of 50 dB (at 50 μm thickness) without requiring any post-processing reduction. Systematic experiments with varying durations of phosphoric acid intercalation establish that a 10-minutes treatment produces inks with superior 3D printing fidelity. This innovative approach to graphene ink production enables rapid, continuous, and large-scale manufacturing of lightweight, porous materials, avoiding the need for environmentally harmful reductant chemistries or high-temperature processing. Furthermore, eliminating the reduction step in the fabrication process aligns with industrial demands for energy-efficient production processes and high output rates, marking a significant advancement in the field of materials science and offering promising prospects for applying graphene-based inks in advanced manufacturing technologies. [ABSTRACT FROM AUTHOR]

A carbon-neutral fuel is desired when it comes to solving the issues associated with climate change. A smart approach would be to develop new materials to produce such fuels, which could be integrated with renewables to improve the efficiency (e.g., solid oxide fuel cells (SOFCs) in smart grid and concentrated solar fuel technologies). In this study, we report the utilization of nonstoichiometric perovskite oxides, Ba2Ca0.66Nb1.34−xFexO6−δ (BCNF) (0 ≤x≤ 1), to split CO2 into carbon, carbon monoxide, and oxygen at elevated temperatures. Powder X-ray diffraction shows the chemical stability of double perovskite-type BCNF after being exposed to 2000 ppm CO2 in Ar at 700 °C. Furthermore, all x≤ 0.66 BCNF members exhibit high chemical stability even under pure CO2 at 700 °C. Scanning electron microscopy coupled with energy dispersive X-ray, Raman spectroscopy, temperature programmed oxidation (TPO) and mass spectroscopy (MS), and DFT analyses confirm the formation of solid carbon upon CO2 exposure, which increases with increasing Fe in BCNF. Mössbauer spectroscopy of the as-prepared BCNF shows the presence of Fe3+, Fe4+ and Fe5+. Upon Ar exposure, the higher valent Fe component is reduced to Fe3+ and subsequent oxidation of Fe3+ seems to promote the CO2 reduction. Overall, these promising results of BCNFs, displaying redox activity at significantly lower temperatures compared to state-of-the-art ceria for CO2 reduction, show great potential for their use in renewable-driven fuel technologies. [ABSTRACT FROM AUTHOR]