RESUMEN
Electrosynthesis of value-added chemicals, directly from CO2, could foster achievement of carbon neutral through an alternative electrical approach to the energy-intensive thermochemical industry for carbon utilization. Progress in this area, based on electrogeneration of multicarbon products through CO2 electroreduction, however, lags far behind that for C1 products. Reaction routes are complicated and kinetics are slow with scale up to the high levels required for commercialization, posing significant problems. In this review, we identify and summarize state-of-art progress in multicarbon synthesis with a multiscale perspective and discuss current hurdles to be resolved for multicarbon generation from CO2 reduction including atomistic mechanisms, nanoscale electrocatalysts, microscale electrodes, and macroscale electrolyzers with guidelines for future research. The review ends with a cross-scale perspective that links discrepancies between different approaches with extensions to performance and stability issues that arise from extensions to an industrial environment.
RESUMEN
A monolithic supercapacitor electrode of a KNi0.67Co0.33PO4·H2O-graphene composite hydrogel supported on Ni foam (KNCP-GH/NF) is first prepared by a one-step hydrothermal method, which achieves notable improvements in the electrode surface area and mass-loading of active materials. The KNCP-GH/NF electrode enjoys a hierarchical open-porous structure, where the KNCP-GH composite hydrogel fills in the voids in NF and the porous graphene hydrogel (GH) simultaneously provides a large support surface for growing active KNCP nanoflowers. Accordingly, the KNCP-GH/NF electrode exhibits a strikingly high capacity of 3240 mC cm-2 (876 C g-1) at 2 mA cm-2 and a satisfactory rate performance with 78.3% retention at 100 mA cm-2. Further, an all-solid-state asymmetric supercapacitor, constituted by using KNCP-GH/NF and Fe2P/GH/NF as the cathode and anode, respectively, and PVA-KOH as the solid-state gel electrolyte, delivers a high energy density of 69.2 W h kg-1 (3.9 mW h cm-3) and a power density of 13 229 W kg-1 (720 mW h cm-3) as well as notable cyclability with 81.2% capacity retention after 10 000 charge/discharge cycles. These attractive performances suggest a promising potential for a hierarchically structured KNCP-GH/NF electrode for the high-performance energy storage application.
RESUMEN
Battery-type materials (e.g., transition metal phosphates) have been intensely explored in supercapacitors due to their rich electroactive sites and high theoretical capacity. Yet poor rate performance, resulting in a low energy density at high current density, limits their further applications. Herein, an improvement in rate performance resulting from enhanced surface capacitive behaviour contribution has been observed in a hierarchically structured Co3(PO4)2/Ni-Co-O@Ni foam (CPNO-12). The optimized CPNO-12 synthesized through a facile hydrothermal treatment also exhibits a striking gravimetric and areal capacity of 1410C g-1 (14 100 mC cm-2) at 5 mA cm-2 and superb cyclability (91% of retention at 50 mA cm-2 after 12 000 cycles), which can be attributed to its unique hierarchical porous structure and high mass loading per area. More importantly, a high-performance all-solid-state asymmetric supercapacitor with CPNO-12 and Fe2P/graphene hydrogel@Ni foam as positive and negative electrodes respectively has been assembled; the device delivering a maximum energy density of 95 W h kg-1 (32 mW h cm-3) and maximum power density of 4000 W kg-1 (800 mW cm-3) has the potential to power sophisticated systems. These attractive performances confirm that an enhancement of capacitive behaviour in battery-type materials holds the promise for fabricating high-performance supercapacitors.