CoOx @NiMoN/Ti3 C2 Tx Interface for Stable High-Performance Electrochemical Energy Storage Devices

Transition metal nitrides (TMNs) are promising electrode materials for use in high-performance electrochemical energy storage devices due to their unique properties, which include a high conductivity, pseudocapacitance, and energy density. However, structural instability during electrochemical reactions has limited their practical deployment for energy storage devices. In this context, the present study fabricated a CoOx @NiMoN/Ti3 C2 Tx electrode via in situ growth on Ni foam using hydrothermal treatment with post-nitrogenization. The effect of atomic layer deposition (ALD) of CoOx on the TMN/Ti3 C2 Tx interface and the consequent electrochemical charge storage mechanisms are investigated in detail. The proposed CoOx @NiMoN/Ti3 C2 Tx electrode delivers an impressive specific capacity in a 2 m potassium hydroxide (KOH) electrolyte and is then employed in both a hybrid solid-state supercapacitor (HSSC) with reduced graphene oxide and a symmetric SC in a 2 m KOH + polyvinyl alcohol (PVA) gel electrolyte. Outstanding charge storage and high capacity retention during cyclic testing are observed for both energy storage devices. The exceptional electrochemical performance of the fabricated electrode is a result of its high conductivity and high number of active sites. Here a feasible new strategy is demonstrated for the fabrication of stable energy storage devices with a high energy density using TMNs and MXenes.

Boosting Pseudocapacitive Behavior of Supercapattery Electrodes by Incorporating a Schottky Junction for Ultrahigh Energy Density

Pseudo-capacitive negative electrodes remain a major bottleneck in the development of supercapacitor devices with high energy density because the electric double-layer capacitance of the negative electrodes does not match the pseudocapacitance of the corresponding positive electrodes. In the present study, a strategically improved Ni-Co-Mo sulfide is demonstrated to be a promising candidate for high energy density supercapattery devices due to its sustained pseudocapacitive charge storage mechanism. The pseudocapacitive behavior is enhanced when operating under a high current through the addition of a classical Schottky junction next to the electrode-electrolyte interface using atomic layer deposition. The Schottky junction accelerates and decelerates the diffusion of OH‒/K+ ions during the charging and discharging processes, respectively, to improve the pseudocapacitive behavior. The resulting pseudocapacitive negative electrodes exhibits a specific capacity of 2,114 C g-1 at 2 A g-1 matches almost that of the positive electrode's 2,795 C g-1 at 3 A g-1. As a result, with the equivalent contribution from the positive and negative electrodes, an energy density of 236.1 Wh kg-1 is achieved at a power density of 921.9 W kg-1 with a total active mass of 15 mg cm-2. This strategy demonstrates the possibility of producing supercapacitors that adapt well to the supercapattery zone of a Ragone plot and that are equal to batteries in terms of energy density, thus, offering a route for further advances in electrochemical energy storage and conversion processes.

Three-Dimensional Hierarchical Core/shell Electrodes Using Highly Conformal TiO2 and Co3O4 Thin Films for High-Performance Supercapattery Devices

The rational design and development of novel electrode materials with promising nanostructures is an effective technique to improve their supercapacitive performance. This work presents high-performance core/shell electrodes based on three-dimensional hierarchical nanostructures coated with conformal thin transition-metal oxide layers using atomic layer deposition (ALD). This effective interface engineering creates disorder in the electronic structure and coordination environment at the interface of the heteronanostructure, which provides many more reaction sites and rapid ion diffusion. At 3 A g^-1, the positive CuCo₂O₄/Ni₄Mo/MoO₂@ALD-Co₃O₄ electrode introduced here exhibits a specific capacity of 1029.1 C g^-1, and the fabricated negative Fe₃O₄@ALD-TiO₂ electrode significantly outperforms conventional carbon-based electrodes, with a maximum specific capacity of 372.6 C g^-1. The supercapattery cell assembled from these two interface- and surface-tailored electrodes exhibits a very high energy density of 110.4 W h kg^-1 with exceptional capacity retention over 20,000 cycles, demonstrating the immense potential of ALD for the next generation of supercapacitors.