CO2 Electrolyzers.

CO2 electrolyzers have progressed rapidly in energy efficiency and catalyst selectivity toward valuable chemical feedstocks and fuels, such as syngas, ethylene, ethanol, and methane. However, each component within these complex systems influences the overall performance, and the further advances needed to realize commercialization will require an approach that considers the whole process, with the electrochemical cell at the center. Beyond the cell boundaries, the electrolyzer must integrate with upstream CO2 feeds and downstream separation processes in a way that minimizes overall product energy intensity and presents viable use cases. Here we begin by describing upstream CO2 sources, their energy intensities, and impurities. We then focus on the cell, the most common CO2 electrolyzer system architectures, and each component within these systems. We evaluate the energy savings and the feasibility of alternative approaches including integration with CO2 capture, direct conversion of flue gas and two-step conversion via carbon monoxide. We evaluate pathways that minimize downstream separations and produce concentrated streams compatible with existing sectors. Applying this comprehensive upstream-to-downstream approach, we highlight the most promising routes, and outlook, for electrochemical CO2 reduction.

Sustainable valorization of asphaltenes via flash joule heating.

The refining process of petroleum crude oil generates asphaltenes, which poses complicated problems during the production of cleaner fuels. Following refining, asphaltenes are typically combusted for reuse as fuel or discarded into tailing ponds and landfills, leading to economic and environmental disruption. Here, we show that low-value asphaltenes can be converted into a high-value carbon allotrope, asphaltene-derived flash graphene (AFG), via the flash joule heating (FJH) process. After successful conversion, we develop nanocomposites by dispersing AFG into a polymer effectively, which have superior mechanical, thermal, and corrosion-resistant properties compared to the bare polymer. In addition, the life cycle and technoeconomic analysis show that the FJH process leads to reduced environmental impact compared to the traditional processing of asphaltene and lower production cost compared to other FJH precursors. Thus, our work suggests an alternative pathway to the existing asphaltene processing that directs toward a higher value stream while sequestering downstream emissions from the processing.

Improved synthesis of Ti3C2Tx MXenes resulting in exceptional electrical conductivity, high synthesis yield, and enhanced capacitance.

For the first time, an "Evaporated-Nitrogen" Minimally Intensive Layer Delamination (EN-MILD) synthesis approach is reported to synthesize exceptionally high quality MXene sheets. In the EN-MILD method, the concentrations of acids and Li-ions are continuously increased during the etching process. By implementing the EN-MILD approach, the electrical conductivity increases up to 2.4 × 104 S cm-1, which is the highest reported value to date for Ti3C2Tx MXenes (a traditional MILD approach results in a conductivity of 5.8 × 103 S cm-1). This significant improvement in electrical conductivity arises from the high quality of the synthesized MXene sheets as well as a larger flake size. The EN-MILD synthesis approach also offers high yield of delaminated single MXene layers (up to ∼60% after the first round of washing/centrifugation) and high colloidal concentrations (up to 31 mg ml-1). The working electrode prepared from free-standing MXene paper shows an exceptional capacitance of ≈490 F g-1 at 1 A g-1 in a supercapacitor, which is among the highest values reported for MXene-based supercapacitor electrodes. The exceptional electrical conductivity, high yield of delaminated MXene single layers, and high colloidal concentration of the EN-MILD approach significantly expand the applications of MXenes.

High Dielectric Constant and Low Dielectric Loss via Poly(vinyl alcohol)/Ti3C2T x MXene Nanocomposites.

As a new class of two-dimensional materials, the MXene family has triggered attention because of its unique electrical and mechanical properties. MXene's excellent electrical conductivity and hydrophilicity make it an ideal option for polymer nanocomposite fabrication. For the first time, polymer nanocomposites of polyvinyl alcohol (PVA)/Ti3C2T x (MXene) were used for charge storage applications in the X-band frequency range (8.2-12.4 GHz). By implementing solution casting and vacuum-assisted filtration (VAF), flexible thin films with exceptional dielectric properties (solution casting @ 10.0 wt % MXene: ε' = 370.5 and tan δ = 0.11 and VAF @ 10.0 wt % MXene: ε' = 3166 and tan δ = 0.09) were fabricated. The reported dielectric constants in this study are among the highest values obtained in X-band frequency with low dielectric losses. This outstanding performance originates from the high electrical conductivity of synthesized Ti3C2T x MXene (σ ≈ 1.4 ± 0.077 × 106 S/m; the highest reported value for Ti3C2T x MXene to date in the literature), great dispersion state, and the nacre-like structure of the polymer nanocomposites. Combining the exceptional properties of MXene with the effective nacre-like structure, PVA/MXene nanocomposites can be used as a novel charge storage material, fulfilling the requirements of flexible electronics and energy storage devices.