Low-cost and high performance electrode materials are critical for rapid development and wide applications of supercapacitors. Herein, we report a costeffective approach to prepare nitrogen-doped active carbon/ graphene (N-AC/Gr) composites using renewable corn straw and soy protein as precursors, respectively. The as-prepared composites have moderate specific surface areas in a range of 1233.6−1412.9 m 2 g −1 and abundant porosity. Furthermore, the composites demonstrate high single electrode gravimetric and volumetric specific capacitances of 378.9 F g −1 and 257.7 F cm −3 at 0.05 A g −1 and of 321.1 F g −1 and 213.2 F cm −3 at 20 A g −1 , accounting for an excellent rate capability with a retention of 66.4% in 6 M KOH electrolyte. The assembled N-AC/Gr-based aqueous symmetric supercapacitor exhibits superior cycling durability with 93% retention after 10,000 cycles at 2 A g −1 and delivers a high energy density of 13.1 Wh kg −1 (11.1 Wh L −1 ) with a power density of 12.5 W kg −1 (10.6 W L −1 ).

The isostructural compounds Yb 2 MgSi 2 , La 2.05 Mg 0.95 Si 2 , and Ce 2.05 Mg 0.95 Si 2 , as well as Yb 2 Li 0.5 Ge 2 and Yb 1.75 Mg 0.75 Si 2 , respectively, were synthesized from stoichiometric mixtures of the corresponding elements in sealed Nb-ampoules under argon atmosphere. The structures were determined by single crystal X-ray diffraction: Yb 2 MgSi 2 (P4/mbm (

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