The development of cost-effective electrocatalysts for overall water splitting is highly desirable, remaining a critical challenge at current stage. Herein, a class of composite FeNi@MXene (Mo₂TiC₂T_x)@nickel foam (NF) has been synthesized through introducing Fe²⁺ ions and in-situ combining with surface nickel atoms on nickel foam. The obtained FeNi@Mo₂TiC₂T_x@NF exhibited high activity with overpotentials of 165 and 190 mV for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) at a current density of 10 mA·cm^-2, respectively. The synergetic effects of Mo₂TiC₂T_x and FeNi nanoalloys lead to increasing catalytic activities, where MXene provides high active surface area and rich active sites for HER, and FeNi nanoalloys promote the OER. Theoretical simulation of electron exchange capacity between FeNi and MXene in FeNi@Mo₂TiC₂T_x catalyst shows that electrons transferred from surface Mo atoms to the interface between FeNi and MXene, indicating that the electrons are accumulated near the FeNi nanoparticles. This kind of electronic distribution facilitates the formation of intermediate of NiOOH. Correspondingly, (H⁺ + e^-) is more inclined onto Mo–Ni interfaces for HER. The Gibbs free energy changes for H* to HER and potential-limiting step for -OOH intermediate in OER over FeNi@Mo₂TiC₂T_x are much less than those on bare MXene. The catalyst can be further used for overall water splitting in alkaline solution, realizing a current density of 50 mA·cm^-2 at 1.74 V. This work provides a facile strategy to achieve efficient and cheap catalysts for new energy production.

The direct electrochemical conversion of CO₂ to syngas with controllable composition remains challenging. In this work, driven by concentration gradient, a simple air-heating aided strategy has been developed to adjust surface composition of the self-supporting nanoporous AuCu₃ alloy. According to Fick First Law, the interior Cu atoms of the AuCu₃ alloy with Au-rich surface gradually segregated outwards during heating, realizing Cu-rich surface eventually. Correspondingly, the competing electrocatalytic CO₂ reduction (ECR) to CO and hydrogen evolution reactions (HER) were tactfully balanced on these alloy surfaces, thus achieving proportion-tunable syngas (CO/H₂). Density functional theory (DFT) calculations on the Gibbs free energy change of the COOH* and H* (ΔG_COOH*, ΔG_H*) on the alloy surfaces were conducted, which are generally considered as the selectivity descriptors for CO and H₂ products, respectively. It shows ΔG_COOH* gradually increases in contrast to the decreased ΔG_H* with more Cu on the surface, suggesting H₂ is more favored over Cu sites, which is consistent with the declining CO/H₂ ratio observed in the experiments. This study reveals that the surface composition controls ECR activity of nanoporous AuCu₃ alloy, providing an alternative way to the syngas production with desirable proportion.

Significant efforts have been directed towards the preparation and application of porous hierarchically structured materials owing to their large surface area, rich active sites, and enhanced mass transport and diffusion. In this study, a simple and cost-effective method for the carbon quantum dot (CQD)-induced assembly of two-dimensional ultrathin Ni(OH)₂ nanosheets into a three-dimensional (3D) porous hierarchical structure was developed. The electrostatic forces between the CQDs and cations drove the self-assembly of the 3D CQDs/Ni(OH)₂ hierarchical structures. As a new type of structure-directing agent, the CQDs played dual roles in tuning the morphology of the products and improving the supercapacitor performance. The multilevel CQDs/Ni(OH)₂ micro-nanostructures had a large specific surface area and rich porosity. Owing to their unique structures and the conductivity of the CQDs, an optimized asymmetric supercapacitor using the CQDs/Ni(OH)₂ exhibited a maximum specific capacity of 161.3 F·g^–1 and a high energy density of 57.4 Wh·kg^–1. This study introduces a potential method for the fabrication of many other 3D hierarchical structures with great potential for applications in various fields.