Jayaraman Jayabharathi

The pursuit of highly efficient, pollution-free hydrogen generation using bifunctional electrocatalysts composed of rare-earth and non-noble metals is of paramount importance.

The benefits of intrinsic sensitivity, speed, cost, and simplicity remain to be robust dynamic forces toward the progress of electrochemical (bio) sensors. In this comprehensive review, the breakthrough ultrasensitive electrochemical sensing performances of emerging efficient sensors for the calendar year up to 2025 have been explored. The goal of this effort is to provide progress in electrode engineering and patterns for electrochemical signal amplification used in sensors. Also, we reviewed enzyme-based biosensors, immunosensors, genosensors, cytosensors, and small molecules. The novel strategies are crucial for the progress of electrochemical sensors, which paves a path for future research. This review provides a roadmap for the advancement of metal-based sensing materials with various techniques. However, we express regret to authors of key publications that were inadvertently left out. Only the original and review articles published in available journals were considered, whereas patents, book chapters, or book serials were omitted for this review.

Scalable synthesis of efficient electrocatalysts with sustained activity remains a major challenge for practical water splitting. Herein, we report a confined mechanochemical strategy for the ultrafast and scalable synthesis of mesoporous (Co–Mo)S heterostructures with abundant interfacial sites. The optimized catalyst exhibits excellent bifunctional performance, delivering overpotentials of 150 mV (HER) and 311 mV (OER) with low Tafel slopes (74 mV dec^–1) and minimal charge-transfer resistance (3.8 Ω). High Faradaic efficiencies (96% for HER and 98% for the OER) confirm efficient charge utilization. Kinetic analyses reveal accelerated electron-transfer dynamics, supported by in situ electrochemical impedance spectroscopy (EIS) and reduced activation energy derived from Arrhenius studies, while trumpet plot analysis indicates enhanced rate constants across varying pH. The catalyst also demonstrates promising oxygen reduction reaction (ORR) activity and robust durability. Notably, an alkaline electrolyzer assembled with (Co–Mo)S requires only 1.58 V to achieve 10 mA cm^–2, highlighting its practical potential. This work demonstrates that interfacial engineering in (Co–Mo)S heterostructures enables efficient charge transfer and improved catalytic kinetics, offering a scalable pathway for advanced electrocatalysts toward sustainable hydrogen production.

Replacing noble metal-based OER electrocatalysts demands economical and high-performance alternatives for energy saving industrial applications. This study explores an innovative combustion synthetic technique to produce a Co₃O₄–CoO (CoOPE-600) heterophase using pomegranate peel extract as a green source of fuel. The optimized CoOPE-600 electrocatalyst showed outstanding electrochemical performance for oxygen evolution reaction (OER), requiring an overpotential of 231 mV to achieve 10 mA cm⁻². The kinetics of CoOPE-600 electrolysis was examined via impedance analysis, demanding a very small activation energy of 5.2 kJ mol⁻¹ compared to Co₃O₄-600 (6.4 kJ mol⁻¹) to complete the reaction, as supported by an Arrhenius plot. The combined contribution of CoO and Co₃O₄ phases increased the catalytically active surface area to expose abundant active sites, increased oxygen vacancies and promoted intimate contact between CoOPE-600 and the electrolyte to facilitate charge transfer around Co active sites for remarkable activity. An alkaline-/solar-driven electrolyzer fabricated with the anode CoOPE-600 required 1.56 V along with notable long-term stability, indicating promising prospects for practical applications. The current research provides a novel green approach for the synthesis of an efficient non-precious electrocatalyst for water splitting.

A polyaniline-coupled cobalt carbonate hydroxide (CoCHCN) electrocatalyst was rationally designed to regulate interfacial charge transport and accelerate the oxygen evolution reaction (OER) kinetics. Structural, morphological, and spectroscopic analyses confirm the uniform coating and strong electronic interaction between polyaniline (CN) and cobalt carbonate hydroxide (CoCH), generating abundant accessible active sites and improved electrical conductivity. In 1 M KOH, CoCHCN achieves a low overpotential of 282 mV at 10 mA cm^-2 and a small Tafel slope of 48 mV dec^-1, reflecting rapid reaction kinetics and favorable reaction pathways. The catalyst exhibits outstanding operational stability for 120 h with negligible potential decay, low charge transfer resistance (3.8 Ω), and a high electrochemically active surface area, enabling efficient electron transfer. Arrhenius analysis reveals a reduced activation energy after CN coupling, confirming kinetically promoted OER processes. Furthermore, an alkaline and solar-driven electrolyzer assembled with a CoCHCN anode delivers 10 mA cm^-2 at 1.58 V, demonstrating practical applicability. This work highlights that conductive polymer coupling is an effective strategy to enhance electron-ion transport and improve scalable water oxidation performance.

Searching for an efficient electrocatalyst remains a major challenge for hydrogen production in the commercial application of water splitting. Herein, we report newly designed material of Res(Ce)-TMs(Ni) carbonate hydroxide embedded...

To regulate transition metal (TM)-based electrocatalysis, rare earth (RE) elements have emerged as key promoters; however, investigation into the RE-enhanced activity of TMs in water splitting reactions is limited. Herein, we used the expired metformin (MF) drug as an organic host to synthesize an RE-TM carbonate hydroxide (MF-CeCoCH) to explore the origin of the Ce-triggered kinetics of Co sites in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The Ce-coupling with MF-CoCH increased the active surface area to expose more active sites and regulated the electronic redistribution of Co sites to boost the specific activity. MF-CeCoCH exhibits exceptional activity with a high durability. The reaction kinetics of the catalysis was monitored via in situ electrochemical impedance spectroscopy (EIS) and the demand for less activation energy after Ce-coupling was revealed by Arrhenius. The doped bimetal cations showed a smaller energy of activation (E_a), analogous to higher activity, yet site reconstruction is less likely to occur. The higher rate constant derived from the Trumpet plot for MF-CeCoCH at various pH values indicates the vigorous formation of gas bubbles. Alkaline and solar-driven electrolyzers of MF-CeCoCH^(*,-) have been explored for total water splitting at 1.58 V, giving an output of 10 mA cm^-2. The exceptional Ce-4f valence electronic structure endows Co sites with differentiated regulation of HER and OER via Ce-4f-Co-3d orbital coupling. In HER, the retained Ce-4f state triggered *H intermediate adsorption, while in OER, the Ce-4f band was sacrificed and provided additional spin coupling with O-intermediates.

Electrocatalytic water splitting depends significantly on the strategic design of efficient and durable catalysts that are cost-effective and composed of earth-abundant materials. To this end, a highly active electrocatalyst is essential for driving the OER process. This research work established a clear and accessible strategy for fabricating a metal oxide electrocatalyst functionalized with a conductive polymer, NiMoO-NC, synthesised by in situ oxidative polymerization aimed at advancing its application in water splitting. The generated NiMoO-NC/NF electrocatalyst exhibited overpotential and Tafel values of around 251 mV and 48 mV dec⁻¹ at 10 mA cm⁻². The stability of the electrocatalyst for OER activity was retained for up to 80 h. The kinetic study via operando EIS inferred less resistance with high conductivity to improve the OER kinetics of NiMoO-NC. Furthermore, the exceptional OER activity was confirmed by Bode analysis. The temperature-dependent analyses inferred that NiMoO-NC showed a lower activation energy of 5.1 kJ mol⁻¹ to promote the kinetics. The as-designed NiMoO-NC electrocatalyst shows great potential for advanced hydrogen technologies owing to its efficient electron transfer capability, excellent stability and high performance in the water oxidation process.