In recent years, supercapacitors have been widely used in the fields of energy, transportation, and industry. Among them, electrical double-layer capacitors (EDLCs) have attracted attention because of their dramatically high power density. With the rapid development of computational methods, theoretical studies on the physical and chemical properties of electrode materials have provided important support for the preparation of EDLCs with higher performance. Besides the widely studied double-layer capacitance (C_D), quantum capacitance (C_Q), which has long been ignored, is another important factor to improve the total capacitance (C_T) of an electrode. In this paper, we survey the recent theoretical progress on the C_Q of two-dimensional (2D) electrode materials in EDLCs and classify the electrode materials mainly into graphene-like 2D main group elements and compounds, transition metal carbides/nitrides (MXenes), and transition metal dichalcogenides (TMDs). In addition, we summarize the influence of different modification routes (including doping, metal-adsorption, vacancy, and surface functionalization) on the C_Q characteristics in the voltage range of ±0.6 V. Finally, we discuss the current difficulties in the theoretical study of supercapacitor electrode materials and provide our outlook on the future development of EDLCs in the field of energy storage.

An urgent and key problem in hydrogen evolution reaction (HER) is to prepare low-cost catalysts with activity comparable to that of platinum (Pt), an intrinsic large number of active sites, and high electrical conductivity. Two-dimensional materials as HER catalysts demonstrate unique advantages. Here, we make first-principles swarm-intelligence structure search calculations to identify a hitherto unknown FeP₃ monolayer with a number of desirable properties. The FeP₃ monolayer shows metallicity and has a high density of states at the Fermi level, showing excellent electrical conductivity. Its HER activity is comparable to that of Pt in view of its low hydrogen adsorption Gibbs free energy and large number of active sites, originating from the more exposed and negatively charged P atoms. More interestingly, the FeP₃ monolayer maintains high HER activity under a biaxial strain of 4%. All these appealing properties make the predicted FeP₃ monolayer a promising candidate for application in HER. Moreover, the relationship between HER activity and P content in FeP_x (x = 1–4) monolayers is explored, providing useful information for designing HER catalysts.