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Suffering from the competitive relationship between the abundant electrochemically active sites and the fast ion transfer channel, it still faces tremendous challenges in simultaneously designing and preparing biomass-derived carbons with excellent capacitive and rate performance. Herein, a dual-activation strategy of KOH and KMnO 4 is used to prepare cotton stalks-derived porous carbon with large specific surface area (SSA) (1634 m 2 g −1 ), interconnected network structure, as well as rational mesopores and micropore ratio. Consequently, the obtained sample exhibits an ultrahigh specific capacitance of 318 F g −1 at 1 A g −1 , 71% capacitance retention at current density up to 50 A g −1 , and only 2% capacitance dissipation in a two-electrode system in 6 M KOH after 10 000 cycles. Importantly, the obtained sample also shows a high areal capacitance of 3.8 F cm −2 under a high mass loading of 16 mg cm −2 . Moreover, the obtained sample also delivers a high energy density of 19.9 Wh kg −1 at 397 W kg −1 in the symmetric two-electrode system using 1 M Na 2 SO 4 aqueous electrolyte. This work provides an alternative avenue for the facile and scaled-up conversion of earth-abundant agricultural wastes into advanced carbon materials for supercapacitors application.

As a promising energy conversion system, zinc air battery (ZABs) usually suffers from short cycle life and poor reversibility due to the slow kinetics of the redox reaction on the air cathode, making it a big-barriers in practical applications. Herein, three-dimensional (3D) porous Co3O4/graphdiyne oxide (GDYO) hybrid nanomaterials with sea urchin-like structures have been prepared by in-situ epitaxial growth. The 3D porous Co3O4/GDYO hybrid nanomaterials with sea urchin-like structures expand the larger contact area between the electrolyte and the electrode, which provide abundant channels for ion diffusion and electron transport with enhanced charge transfer kinetics and structural stability. The 3D porous Co3O4/GDYO hybrid nanomaterials with sea urchin-like structures shows excellent bifunctional electrocatalytic activity for both OER (onset potential of 1.38 V, overpotential of 335 mV at 10 mA cm-2) and ORR (onset potential of 0.84 V, half-wave potential of 0.6 V). ZABs fabricated with 3D porous Co3O4/GDYO hybrid nanomaterials as cathode display a high power density of 96 m W cm-2, an open circuit voltage of 1.53 V, as well as a specific capacity of 799.5 mA h g-1 (at 10 mA cm-2) and a corresponding energy density of 965 W h kg-1. Further, its charge and discharge voltages remain stable for over 400 hours at a constant current charge-discharge cycling of 3 mA cm-2. This work offers novel insights on developing excellent bifunctional electrocatalysts for both OER and ORR, which expands a new application of graphdiyne oxide on ZABs.