Dual modulation of the morphology and electric conductivity of NiCoP on nickel foam by Fe doping as a superior stability electrode for high energy supercapacitors

Cr doping and heterostructure-accelerated NiFe LDH reaction kinetics assist the MoS2 oxygen evolution reaction

Although molybdenum disulfide (MoS2) has garnered significant interest as a potential catalyst for the oxygen evolution reaction (OER), its poor intrinsic activity and few marginal active spots restrict its electrocatalytic activity. Herein, we successfully constructed a catalyst via a simple hydrothermal method by forming a heterostructure of MoS2 with Cr-doped nickel-iron hydroxide (NiFe LDH) to synthesize a MoS2/NiFeCr LDH catalyst to significantly improve the OER catalytic performance. MoS2 plays a crucial function as an electron transport channel in the MoS2/NiFeCr LDH heterostructure, which increases the electron transport rate. Furthermore, a larger active surface area for NiFeCr LDH is provided by the ultrathin layered structure of MoS2, increasing the number of active sites and encouraging the OER. On the other hand, the introduction of Cr element increased the density of the catalytic center and provided additional Cr-OH active sites, which accelerated the oxygen decomposition reaction. These two factors act synergistically to improve the intrinsic structure of MoS2, increase the number of reactive sites, and dramatically enhance the OER catalytic performance. Excellent OER activity is demonstrated by the MoS2/NiFeCr LDH catalyst, which only needs an overpotential of 224 mV to obtain a current density of 10 mA cm-2 and a Tafel slope of 61 mV dec-1. The catalyst also demonstrated outstanding stability, with its activity practically holding steady after 48 h of testing. This work offers novel ideas for enhancing and designing MoS2-based OER catalysts, and it provides a crucial reference for research in the field of clean energy.

Iron-doped nickel-cobalt bimetallic phosphide nanowire hybrids for solid-state supercapacitors with excellent electromagnetic interference shielding

The development of flexible and wearable electronics subjects to the limited energy density and accompanying electromagnetic pollution. With a high theoretical specific capacity, nickel-cobalt bimetallic phosphide (NiCoP) is considered to be potential cathode materials for supercapacitor. However, the pristine NiCoP fails to display excellent electrochemical performance due to its inferior rate performance and cycling stability. Herein, we design Fe doped NiCoP nanowire arrays on carbon cloth (Fe-NiCoP/CC) as the cathode for supercapacitors. The introduced Fe doping enable to increase in the electronic conductivity and enhance the adsorption of OH-, supported by the density functional theory (DFT) analysis. As a result, Fe-NiCoP/CC electrode displays a high areal capacity of 3.18 F cm-2 at 1 mA cm-2, superb rate capability (86.3 % capacity retention at 20 mA cm-2) and outstanding structure stability, superior to the NiCo/CC, FeNiCo/CC, and NiCoP/CC counterparts. Moreover, the assembled Fe-NiCoP/CC||VN/CNT/CC hybrid supercapacitor (HSC) device delivers a high energy density of 176.9 μWh cm-2 at the power density of 750 μW cm-2. More importantly, the designed electrodes and assembled HSC device exhibits excellent electromagnetic interference (EMI) shielding performance. This design concept presented in this paper can provide insights into the construction of multifunctional and high-performance flexible electronic devices.

Porous prussian blue analogs derived nickel-iron bimetallic phosphide nanocubes on conductive hollow mesoporous carbon nanospheres for stable and flexible high-performance supercapacitor electrode

Nickel-iron bimetallic phosphide (Ni-Fe-P) is the ideal battery-type materials for supercapacitor in virtue of high theoretical specific capacitance. Nevertheless, its actual adhibition is astricted on account of inferior rate capability and cyclic stability. Herein, we constructed hierarchical core-shell nanocomposites with hollow mesoporous carbon nanospheres (HMCS) packaged via prussian blue analogs derived Ni-Fe-P nanocubes (Ni-Fe-P@HMCS), as a positive electrode for hybrid supercapacitor (HSC). Profiting from the cooperative effects of Ni-Fe-P nanocubes with small size and good dispersibility, and HMCS with continuously conductive network, the Ni-Fe-P@HMCS composite electrode with abundantly porous architectures presents an ultrahigh gravimetric specific capacity for 739.8 C g-1 under 1 A g-1. Specially, the Ni-Fe-P@HMCS electrode presents outstanding rate capability of 78.4% (1 A g-1 to 20 A g-1) and cyclic constancy for 105% after 5000 cycles. Density functional theory implies that the composite electrode possesses higher electrical conductivity than bare Ni-Fe-P electrode by reason of the incremental charge density, and the electrons transferring from NiFe3P4 to HMCS layers. Additionally, the assembled Ni-Fe-P@HMCS//HMCS HSC facility delivers the high energy density for 64.1 Wh kg-1, remarkable flexibility and mechanical stability. Thus, this work proffers a viable and efficacious measure to construct ultra-stability electrode for high-performance portable electronic facilities.

Oxygen-doped NiCoP derived from Ni-MOFs for high performance asymmetric supercapacitor

Oxygen doping strategy is one of the most effective methods to improve the electrochemical properties of nickel-cobalt phosphide (NiCoP)-based capacitors by adjusting its inherent electronic structure. In this paper, O-doped NiCoP microspheres derived from porous nanostructured nickel metal-organic frameworks (Ni-MOFs) were constructed through solvothermal method followed by phosphorization treatment. The O-doping concentration has a siginificant influence on the rate performance and cycle stability. The optimized O-doped NiCoP electrode material shows a specific capacitance of 632.4 F-g-1at 1 A-g-1and a high retention rate of 56.9% at 20 A g-1. The corresponding NiCoP-based asymmetric supercapacitor exhibits a high energy density of 30.1 Wh kg-1when the power density is 800.9 W kg-1, and can still maintain 82.1% of the initial capacity after 10 000 cycles at 5 A g-1.

Sea urchin-like amorphous MgNiCo mixed metal hydroxide nanoarrays for efficient overall water splitting under industrial electrolytic conditions

Exploring amorphous mixed transition metal hydroxide electrocatalysts with high performance and stability for overall water splitting is a difficult challenge under industrial electrolytic conditions. Herein, a sea urchin-like amorphous MgNiCo hydroxide (Mg_xNi_1-xCo-OH, 0 < x < 1), self-assembled from nanowire arrays, is synthesized by the hydrothermal process. The synergistic effect between Mg and Ni/Co adjusts their crystal structure and morphology, which can improve the inherent activity and provide more active sites. Benefiting from the favorable structural features, Mg_0.5Ni_0.5Co-OH exhibits superior electrocatalytic oxygen and hydrogen evolution reaction (OER and HER) activity with a low overpotential of 277 and 110 mV (10 mA cm^-2) in 1 M KOH at 25 °C. Furthermore, overpotentials of 239 and 197 mV are required to achieve a current density of 50 mA cm^-2 for the OER and HER under simulated industrial electrolysis conditions (5 M KOH at 65 °C). Notably, Mg_0.5Ni_0.5Co-OH remarkably accelerates water splitting with a low voltage of 1.938 and 1.699 V for 50 mA cm^-2 in 1 M KOH at 25 °C and 5 M KOH at 65 °C, respectively. This work presents a novel amorphous strategy to design and construct sea urchin-like mixed metal hydroxide bifunctional efficient electrocatalysts for industrial applications.

Fe and P dual-doped nickel carbonate hydroxide/carbon nanotube hybrid electrocatalysts for an efficient oxygen evolution reaction

Designing cost-effective and highly active oxygen evolution reaction (OER) electrocatalysts is critical for large-scale hydrogen production from electrocatalytic water splitting. Herein, Fe and P dual-doped nickel carbonate hydroxide/carbon nanotubes (Fe, P-NiCH/CNTs) were fabricated through a solvothermal method. By virtue of the optimized electronic structure, improved conductivity and enriched active sites, the as-fabricated Fe, P-NiCH/CNT hybrid electrocatalyst exhibits superior OER activity, with a low overpotential of 222 mV at 20 mA cm^-2 and robust durability, confirming its potential as a highly efficient OER electrocatalyst. Moreover, theoretical calculations demonstrate that the doped Fe and surface adsorbed PO₄^3- can regulate the electronic structure of evolved NiOOH and decrease the energy barrier of the rate-determining step, thus leading to improved OER activity. The strategy presented in this work can also be employed to fabricate other transition metal carbonate hydroxides for various electrocatalytic applications.