Thandavarayan Maiyalagan

Highly porous activated carbon was synthesized from Cocos nucifera shell through a one‐step KOH‐assisted pyrolysis process at a carbonization temperature of 700 °C. The structural, microstructural, textural, and electrochemical properties of the prepared Cocos nucifera shell‐derived activated carbon (CAC) and phosphorus‐doped activated carbon (P‐CAC) were systematically investigated. The electrochemical performance of both electrode materials was evaluated in a 3 M NaOH electrolyte using a three‐electrode configuration. The CAC and P‐CAC electrodes exhibited excellent capacitive behavior, delivering specific capacitances of 177.4 and 266.5 F g ⁻¹ , respectively, at a current density of 1 A g ⁻¹ . The enhanced electrochemical performance of the P‐CAC electrode is attributed to the synergistic effect of its hierarchical porous structure, improved surface chemistry, and phosphorus‐induced active sites, which facilitate efficient electrolyte ion transport and charge storage. These findings demonstrate a sustainable and cost‐effective strategy for converting Cocos nucifera shell biomass waste into high‐performance carbon electrode materials, highlighting their potential for application in next‐generation portable and wearable energy storage devices.

The development of high-performance bifunctional electrocatalysts for water splitting is vital for sustainable hydrogen evolution. Herein, an oxygen-incorporated MoS2/NiFe-layered double hydroxide (LDH)/multiwalled carbon nanotube (MWCNT) heterostructure with abundant defect sites was rationally designed and synthesized to enhance the electrocatalytic performance toward both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). X-ray photoelectron spectroscopy (XPS) reveals mixed-valence states and binding-energy shifts, indicating strong interfacial electronic interactions, while electron paramagnetic resonance (EPR) and Raman spectroscopy confirm the presence of defect sites and enhanced structural disorder. These features facilitate charge transfer and optimize the adsorption of reaction intermediates. As a result, the optimized catalyst delivers excellent oxygen evolution reaction (OER) activity with a low overpotential of 204 mV at 10 mA/cm2 and a small Tafel slope of 57 mV dec−1, along with excellent hydrogen evolution reaction (HER) performance requiring only 159 mV at 10 mA/cm2. Remarkably, the catalyst demonstrates exceptional durability with stable 72 h operation for both OER and HER and enables efficient overall water splitting at a low cell voltage of 1.58 V for over 100 h of continuous electrolysis. The overall performance is attributed to the synergistic effect of defect engineering and electronic modulation, making this heterostructure a promising candidate for efficient and durable water-splitting applications.

Developing efficient and robust noble-metal-free electrocatalysts for the hydrogen evolution reaction (HER) under acidic conditions remains a significant challenge. CoS2 was developed as an efficient electrocatalyst for HER, exhibiting superior conductivity and intrinsic catalytic activity. We present Fe-doped CoS2 nano-octahedra synthesized via controlled hydrothermal sulfidation, serving as an effective electrocatalyst for HER. The incorporation of Fe into the pyrite CoS2 lattice alters its electronic configuration, enhances the adsorption energies of hydrogen evolution reaction intermediates, and increases the density of electrochemical active sites. The optimized 8% Fe-doped CoS2 attains a reduced overpotential of 57 mV at 10 mA cm-2 and Tafel slope of 56 mV·dec⁻¹, surpassing that of pristine CoS2 nano-octahedra. The catalyst demonstrates approximately 96 hours of stable performance in 0.5 M H2SO4, highlighting its stability in acidic medium. This study presents a cost-effective and scalable method for developing transition-metal chalcogenides with altered electronic structures to enhance hydrogen generation in acidic conditions.

Significant effort has been taken to improve the Hydrogen Evolution Reaction (HER) to make the hydrogen fuel economy possible. Although Pt based catalysts exhibit excellent HER activity, their high cost and limited availability hinder their largescale application. Therefore, developing efficient, low-cost, and earth-abundant transition metal based electrocatalysts has become an important research focus. This study implements the concept of incorporating oxygen in the Molybdenum Disulfide (MoS2) and making a nanocomposite with Nitrogen and Phosphorus-doped Reduced Graphene Oxide. The O-MoS2/N, P-rGO synthesis strategy involves a facile hydrothermal method for MoS2 and the preparation of heteroatomdoped graphene by high-temperature heating. The resulting composite of O-MoS2 with N, P-rGO outperforms the other O-MoS2-based nanocomposite and bare O-MoS2 towards electrochemical HER activity by exhibiting an onset potential of 110 mV, an overpotential of 160 mV measured at 10 mA/cm2 and a Tafel slope value of 87 mV/dec. The optimized O-MoS2/N, P-rGO exhibits a high current density of 100 mA/cm2 at the minimum overpotential of 250 mV and demonstrates near stable performance with minimal overpotential difference of 20 mV after continuous 1000 cycles.

Structural modification of NiCo LDH to Fe _0.1 Ce _0.1 –NiCoP through phosphidation and Fe/Ce co-doping to enhance the oxygen evolution reaction performance.

The rational design of efficient electrocatalysts for the oxygen evolution reaction (OER), holds the key to advancing the overall electrolytic water splitting performance. Here, a scalable one‐pot synthesis of a stable chromium─iron nickel boride (Cr─FeNiB) electrocatalyst is reported for OER in which nickel‐boron sites are micro‐environmentally modified through interactions with iron and chromium. Comprehensive, correlative electrochemical, structural, and chemical analyses reveal the formation of amorphous‐crystalline core‐shell structures that transform into nanosheets upon activation with enhanced water oxidation catalytic activity. The enhanced catalytic performance is attributed to the chromium‐induced chemical self‐reconstruction of the catalyst, which facilitates favorable OER kinetics, increased turnover frequency, and a synergistic effect between metal and boron constituents. Density Functional Theory (DFT) calculation showed that chromium incorporation effectively shifts the d ‐band centers ( ɛ _d ) closer to the Fermi level and narrows the metal‐d/boron‐p band center gap (Δ ɛ _d‐p ) (Ni ₂ B 1.10 eV → FeNiB 0.71 eV → Cr─FeNiB 0.55 eV) ultimately enhancing OER activity. Accordingly, the Δ ɛ _d‐p is established as a key electronic descriptor for predicting and optimizing OER performance. These findings pave the way for a better understanding of metal boride‐derived electrocatalysts and also contribute to the development of efficient, stable, earth‐abundant, non‐noble metal catalysts for water oxidation.