Al-Based LDH materials have been considered as promising active electrode materials for pseudocapacitors due to their structural tunability. In this work, we employed a hydrothermal method, alkali etching treatment, calcination and sulfofication to achieve crystalline phase transformation. According to this pathway, five materials, including CoAl LDH, Co₂AlO₄, Co(OH)₂, Co₃O₄ and Co₄S₃, have been prepared. The structural and physical/chemical properties are characterized by XRD, XPS, BET, SEM, TEM and FTIR. The electrochemical behaviors in supercapacitor and asymmetric supercapacitor (ASC) devices are characterized, respectively. As the electrode materials in supercapacitors, the specific capacitances are in the order CoAl LDH > Co₄S₃ > Co₂AlO₄ > Co₃O₄ > Co(OH)₂. The CoAl LDH exhibits the maximum specific capacitance due to the intercalation/deintercalation of electrolyte ions which is attributed to its unique layer structure. The CoAl LDH exhibits a high specific capacitance of 983.71 F g⁻¹ at 1 A g⁻¹, a superior rate capability of 79.00% at 20 A g⁻¹ and excellent cycling stability with a capacitance retention of 89.10% after 15 000 cycles. After assembling the ASC device, a maximum energy density of 16.275 W h kg⁻¹ and a high power density of 3500 W kg⁻¹ are achieved in a potential window of 1.4 V. In a word, the study not only provides a dependable pathway for materials modification, but also promotes the development of cobalt-based electrode materials for energy storage.

Graphene oxide (GO) reinforced cement nanocomposites open up a new path for sustainable concrete design. In this paper, reactive force-field molecular dynamics was utilized to investigate the structure, reactivity and interfacial bonding of calcium silicate hydrate (C–S–H)/GO nanocomposite functionalized by hydroxyl (C–OH), epoxy (C–O–C), carboxyl (COOH) and sulfonic (SO₃H) groups with a coverage of 10%. The silicate chains in the hydrophilic C–S–H substrate provided numerous non-bridging oxygen sites and counter ions (Ca ions) with high reactivity, which allowed interlayer water molecules to dissociate into Si–OH and Ca–OH. On the other hand, protons dissociated from the functional groups and transferred to non-bridging sites in C–S–H, producing carbonyl (CO) and Si–OH. The de-protonation degree of the different groups in the vicinity of the C–S–H surface was in the following order: COOH (SO₃H) > C–OH > C–O–C. In the GO–COOH sheet, most COOH groups were de-protonated to COO⁻ groups, which enhanced the polarity and hydrophilicity of the GO sheets and formed stable COOCa bonds with neighboring Ca ions. The de-protonated COO⁻ could also accept H bonds from Si–OH in the C–S–H gel, which further strengthened the interfacial connection. On the contrary, in the GO–Oo sheet, only 8% of the epoxy group was stretched open by the Ca ions and transformed to carbonyl group, showing weak polarity and connection with the C–S–H sheet. Furthermore, uniaxial tensile test on different C–S–H/GO models revealed that C–S–H reinforced with GO–COOH and GO–OH had better interfacial cohesive strength and ductility than that observed under tensile loading. Under the reaction force field, the dissociation of water, the proton exchange between the C–S–H and GO structure, and Oc–Ca–Os bond breakage occurred to resist tensile loading. The weakest mechanical behavior observed in the G/C–S–H, GO–Oo/C–S–H and GO–SO₃H/C–S–H composites was attributed to the poor bonding, dissociation of functional groups and instability of atoms in the interface region. Hopefully, the molecular-scale strengthening mechanisms could provide a scientific guide for sustainable design of cement composites.