Bi-Fe chalcogenides anchored carbon matrix and structured core-shell Bi-Fe-P@Ni-P nanoarchitectures with appealing performances for supercapacitors

Optimum iron-pyrophosphate electronic coupling to improve electrochemical water splitting and charge storage

Tuning the electronic properties of transition metals using pyrophosphate (P2O7) ligand moieties can be a promising approach to improving the electrochemical performance of water electrolyzers and supercapacitors, although such a material's configuration is rarely exposed. Herein, we grow NiP2O7, CoP2O7, and FeP2O7 nanoparticles on conductive Ni-foam using a hydrothermal procedure. The results indicated that, among all the prepared samples, FeP2O7 exhibited outstanding oxygen evolution reaction and hydrogen evolution reaction with the least overpotential of 220 and 241 mV to draw a current density of 10 mA/cm2. Theoretical studies indicate that the optimal electronic coupling of the Fe site with pyrophosphate enhances the overall electronic properties of FeP2O7, thereby enhancing its electrochemical performance in water splitting. Further investigation of these materials found that NiP2O7 had the highest specific capacitance and remarkable cycle stability due to its high crystallinity as compared to FeP2O7, having a higher percentage composition of Ni on the Ni-foam, which allows more Ni to convert into its oxidation states and come back to its original oxidation state during supercapacitor testing. This work shows how to use pyrophosphate moieties to fabricate non-noble metal-based electrode materials to achieve good performance in electrocatalytic splitting water and supercapacitors.

Battery-like bismuth oxide anodes for soft-packed supercapacitors with high energy storage performance

Bismuth compounds are of interest because of abundant reserves and high theoretical capacity for use as anodes in supercapacitors. In this work, bismuth oxycarbonate is synthesized by a hydrothermal method, and bismuth oxide is obtained by the subsequent calcination process, both of which possess high specific capacity. In particular, Bi₂O₃ possesses a specific capacity of 1178 F g^-1 (1178 C g^-1, 327 mA h g^-1) at a current density of 1 A g^-1, and still retains 94.9% capacity at 20 A g^-1, indicating excellent rate capability. Furthermore, Ni(OH)₂ is prepared with a specific capacity of 2447 F g^-1 at 1 A g^-1. Using Bi₂O₃ as the anode and Ni(OH)₂ as the cathode, respectively, the soft-packed supercapacitors are assembled with a large voltage window of 1.75 V. The energy density is as high as 139.7 W h kg^-1 at a power density of 874.8 W kg^-1. Even at 18 000 W kg^-1, the device retains an energy density of 94 W h kg^-1. Connecting two devices in series as a power source can light up 88 light emitting diodes (LEDs) for 2 hours, and drive a tiny fan to run for 18 seconds. The work provides new ways for the practical application of supercapacitors.

NiAlP@Cobalt substituted nickel carbonate hydroxide heterostructure engineered for enhanced supercapacitor performance

Transitional metal phosphides with high electrical conductivity and superb physicochemical features have been recognized as ideal battery-type electrode materials for outstanding performance supercapacitors. However, their specific capacities and structural stability are needed to be enhanced for large-scale practical applications. To overcome these shortcomings, we fabricated heterostructured NiAlP@cobalt substituted nickel carbonate hydroxide (Co-NiCH) nanosheet arrays by sequential a hydrothermal reaction, a phosphorization treatment, and a second hydrothermal reaction. Profiting from its core-shell porous nanostructure and synergistic effect of NiAlP with high electrical conductivity and Co-NiCH with high redox reactivity, the resultant NiAlP@Co-NiCH electrode delivers a large specific capacity of 825.7C g^-1 at 1 A g^-1, excellent rate capability with 78.9% capacity retention and long lifespan, superior to those of pure NiAlP and Co-NiCH electrodes. Additionally, an aqueous asymmetric supercapacitor device is constructed by NiAlP@Co-NiCH and lotus pollen-derived hierarchical porous carbon, which demonstrates a large energy density of 82.3 Wh kg^-1 at a power density of 739.8 W kg^-1, and wonderful cycle stability with 88.2% capacity retention after 10,000 cycles. This work proposes a feasible strategy on construction of transitional metal phosphide-based heterojunctions for advanced asymmetric supercapacitor devices.