Boosted cycling stability of CoP nano-needles based hybrid supercapacitor with high energy density upon surface phosphorization

Activation-Assisted High-Concentration Phosphorus-Doping to Enhance the Electrochemical Performance of Cobalt Carbonate Hydroxide Hydrate

P-doping into metal oxides has been demonstrated as a valid avenue to ameliorate electrochemical performance because it can tune the electronic structures and increase the active sites for an electrochemical reaction. However, it usually results in a low P-doping concentration via the commonly used gas phosphorization method. In this work, an activation-assisted P-doping strategy was explored to significantly raise the P-doping concentration in cobalt carbonate hydroxide hydrate (CCHH). The activation treatment increased active sites for electrochemical reaction and endowed the sample with a high P content in the subsequent gas phosphorization process, thereby greatly enhancing the conductivity of the sample. Therefore, the final CCHH-A-P electrode exhibited a high capacitance of 6.62 F cm^-2 at 5 mA cm^-2 and good cyclic stability. In addition, the CCHH-A-P//CC ASC with CCHH-A-P as the positive electrode and carbon cloth as the negative electrode provided a high energy density of 0.25 mWh cm^-2 at 4 mW cm^-2 as well as excellent cycling performance with capacitance retention of 91.2% after 20,000 cycles. Our work shows an effective strategy to acquire Co-based materials with high-concentration P-doping that holds great potential in boosting the electrochemical performance of electrode materials via P-doping technology.

Atypical performance of CoO-accelerated interface tweaking in hierarchical cobalt phosphide/oxide@P-doped rGO heterostructures for hybrid supercapacitors

Designing two-dimensional (2D) heterostructures based on suitable energy materials is a promising strategy to achieve high-performance supercapacitors with hybridized transition metal and carbonaceous-based electrodes. The influence of each component and its content on the capacitor performance necessitates deeper insights. In this study, a 2D/2D heterostructure made of hierarchical pseudocapacitive cobalt phosphide/oxide and P-doped reduced graphene oxide (PrGO) nanosheets (CoP/CoO@PrGO) was fabricated using porous zeolitic-imidazolate framework precursor. The decoration of 2D leaf-like CoP/CoO hybrid onto PrGO could create a unique interface with a large number of active sites, CoO-driven creation of pseudocapacitive surface PO_x species, and high P content (∼3 at.%) in PrGO, thus promoting the Faradaic reaction, electrical conductivity, and overall charge storage. This framework yields a high specific capacitance of 405 F g^-1 at 5 A g^-1 and excellent cycling stability (over 100 % after 10,000 cycles), superior to those of pristine CoP@PrGO (300 F g^-1 at 5 A g^-1). Furthermore, the fabricated asymmetric supercapacitor delivers reasonable energy density of 4.2 Wh kg^-1 at a power density of 785 W kg^-1 and cycling stability of ∼100 % after 10,000 cycles. Therefore, CoP/CoO@PrGO with its unique interfacial properties can promote the development of heterostructure electrode for high-performance supercapacitors.

Freestanding trimetallic Fe-Co-Ni phosphide nanosheet arrays as an advanced electrode for high-performance asymmetric supercapacitors

Transition metal phosphides hold great promise for high performance battery-type electrode materials due to their superb electrical conductivity and high theoretical capacity. Unfortunately, the electrochemical properties of single metal or bimetallic phosphides are unsatisfactory owing to their low energy density and poor cyclic stability, and one feasible approach is to introduce heteroatoms to form trimetallic phosphides. Here, novel Fe-Co-Ni-P nanosheet arrays are in situ synthesized on a flexible carbon cloth substrate via an electrodeposition method followed by a phosphorization treatment. Due to the presence of abundant redox active sites, large specific surface area with mesoporous channels, desirable electrical conductivity, modified electronic structure, and synergistic effect of Fe, Co, and Ni ions, the as-prepared Fe-Co-Ni-P electrode displays significantly enhanced electrochemical performance when compared to bimetallic phosphides Fe-Co-P and Fe-Ni-P. Remarkably, the Fe-Co-Ni-P electrode exhibits a large specific capacity of 593.0 C g^-1 at 1 A g^-1, exceptional rate performance (80.3% capacity retention at 20 A g^-1), and good cycling stability (84.2% capacity retention after 5000cycles). Besides, an asymmetric supercapacitor device with Fe-Co-Ni-P electrode as a positive electrode and a hierarchical porous carbon as a negative electrode shows a high energy density of 57.1 Wh kg^-1 at a power density of 768.5 W kg^-1 as well as excellent cyclability with 88.4% of initial capacity after 10,000cycles. This work manifests that the construction of trimetallic phosphides is an effective strategy to solve the shortcomings of single or bimetallic phosphides for high-performance supercapacitors.

High-capacity CoP-Mn3P nanoclusters heterostructures derived by Co2MnO4 as advanced electrodes for supercapacitors

Although transition metal oxides (TMOs) have attracted enormous attention owing to their high performance in supercapacitors, it still remains challenging issues in terms of the poor electrical conductivity, sluggish redox kinetics and insufficient electrochemical active sites. Herein, the high-capacity CoP-Mn₃P nanoclusters featuring the heterogeneous interfaces have been successfully synthesized through hydrothermal method followed by annealing. The heterojunction formed between CoP and Mn₃P redistributes the charge at the interface between them, generating the built-in electric field to accelerate electron transfer, and thus the conductivity of the electrode is enhanced. Moreover, the unique morphology of nanoclusters composed of flake structures is beneficial to provide more electrochemical active sites. Consequently, the resultant CoP-Mn₃P nanoclusters electrode delivers an exceptional gravimetric specific capacity (2714 F g^-1 at 1 A g^-1) as well as a long cycle lifespan (83.1% of capacitance retention after 10,000 cycles). An asymmetric supercapacitor (ASC) device assembling with employing CoP/Mn₃P electrode presents an ultrahigh energy density value of 46.4 Wh kg^-1 at a power density of 800.0 W kg^-1 and a super capacitance retention of 86.2% after 30,000 cycles. This work paves an effective way for the investigation on the charge transfer kinetics of electrode materials.

Co2P decorated Co3O4 nanocomposites supported on carbon cloth with enhanced electrochemical performance for asymmetric supercapacitors

An effective strategy is demonstrated to promote electrochemical performance by the combination of Co3O4 with Co2P to form a composite electrode.

Rational synthesis of CoFeP@nickel-manganese sulfide core-shell nanoarrays for hybrid supercapacitors

Transition metal phosphide electrodes, particularly those with unique morphologies and micro-/nanostructures, have demonstrated desirable capabilities for hybrid supercapacitor applications by virtue of their superior electrical conductivity and high electrochemical activity. Here, three-dimensional hierarchical CoFeP@nickel-manganese sulfide nanoarrays were in situ constructed on a flexible carbon cloth via a hydrothermal method, a phosphorization process, followed by an electrodeposition approach. In this smart nanoarchitecture, CoFeP nanorods grown on carbon cloth act as the conductive core for rapid electron transfer, while the nickel-manganese sulfide nanosheets decorated on the surface of CoFeP serve as the shell for efficient ion diffusion, forming a stable core-shell heterostructure with enhanced electrical conductivity. Benefiting from the synergy of the two components and the generation of a heterointerface with a modified electronic structure, The CoFeP@nickel-manganese sulfide electrodes deliver a high capacity of 260.7 mA h g^-1 at 1 A g^-1, excellent rate capability, and good cycling stability. More importantly, an aqueous hybrid supercapacitor based on CoFeP@nickel-manganese sulfide as a positive electrode and a lotus pollen-derived hierarchical porous carbon as a negative electrode is constructed to display a maximum energy density of 60.1 W h kg^-1 at 371.8 W kg^-1 and a good cycling stability of 85.7% capacitance retention after 10 000 cycles.

Core-shell NiSe/Ni(OH)2with NiSe nanorods and Ni(OH)2nanosheets as battery-type electrode for hybrid supercapacitors

Novel core-shell nanostructure electrodes benefit from the excellent properties of their constituent materials, as well as the synergy between them. However, it is challenging to fabricate such structures efficiently. In this study, NiSe nanorods were fabricated using Ni foam as the conductive substrate and reactant via a one-step hydrothermal process, and Ni(OH)₂nanosheets were coated on the surface of the nanorods via one-step electrodeposition. The effect of the structure and morphology on the properties of the material was explored using scanning electron microscopy, x-ray diffraction, and electrochemical technology. The obtained core-shell NiSe/Ni(OH)₂exhibited an areal capacity of 1.89 mAh cm^-2at a current density of 5 mA cm^-2. The assembled NiSe/Ni(OH)₂//AC hybrid supercapacitor exhibited excellent energy and power densities, indicating that NiSe/Ni(OH)₂has great potential for use as a battery-type electrode in energy storage systems.