Rathindranath Biswas

The large-scale deployment of electrochemical CO ₂ conversion requires the development of catalysts that are both highly selective and stable under operating conditions.

Rechargeable metal‐air batteries offer exceptional theoretical energy densities but require durable bifunctional electrocatalysts that efficiently mediate oxygen reduction (ORR) and oxygen evolution (OER). Here, a triazole‐based cobalt complex (CoTzN) is developed to bridge molecular‐level mechanistic understanding with practical device integration. In homogeneous media, CoTzN catalyzes bidirectional ORR/OER, while electrochemical and spectroelectrochemical studies identify key Co(III)–OOH and Co(III)–O• intermediates. These molecular insights guide catalyst heterogenization on carbon nanotubes through π–π interactions (CoTzN‐P) and covalent amide anchoring (CoTzN‐C). CoTzN‐C exhibits enhanced charge transfer, stability across pH 7–14, and a highly selective four‐electron ORR pathway (n ≈ 3.95) with 450 rapid charge‐discharge cycles over ≈30 h, while a non‐aqueous Li‐air battery operates for 80 prolonged cycles (≈160 h). This molecular‐to‐device framework demonstrates how coordination‐level catalyst design can be translated into robust hybrid electrodes for cross‐platform rechargeable metal–air batteries.

Developing efficient, low-cost bifunctional electrocatalysts for overall water splitting is crucial for sustainable hydrogen production via water electrolysis. Herein, a NiS2/CoTe heterostructure with tunable compositional ratios was successfully synthesized via a facile hydrothermal method and systematically investigated for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) applications. Structural characterization revealed that crystalline NiS2 nanoparticles were uniformly anchored on conductive CoTe nanosheets, forming a well-defined nanoscale heterointerface. Among the synthesized catalysts, the optimized NiS2/CoTe-90:10 heterostructure exhibited the highest catalytic activity, requiring overpotentials of only 168 and 363 mV to achieve a current density of 10 mA/cm2 for HER and OER, respectively. NiS2/CoTe-90:10 further exhibited superior long-term durability and high faradaic efficiencies of 98.3 ± 0.5% and 97.8 ± 0.3% for HER and OER, respectively. The catalyst achieved H2 and O2 production rates of 414.3 and 194.4 μmol/h, respectively, while achieving turnover frequency (TOF) of 6.16 × 10−2 s−1 for HER and 12.21 × 10−3 s−1 for OER, representing a twofold and 1.4-fold enhancement over pristine NiS2, respectively. This improved performance originates from the synergistic coupling between NiS2 and CoTe, accelerated interfacial charge transfer, and enlarged electrochemically active surface area. Moreover, a single-stack anion-exchange membrane alkaline electrolyzer using the NiS2/CoTe-90:10 achieved a cell voltage of 1.78 V at 10 mA/cm2. This work provides valuable insights into the nanoscale heterointerface engineering of transition-metal chalcogenides to rationally design next-generation bifunctional electrocatalysts for efficient water splitting.

Vitamin B12 (cobalamin) is an evolutionarily optimized Co-corrin redox cofactor capable of accessing low-valent cobalt states to mediate challenging biological transformations. Here, we reengineer this biological redox platform into an electrode-addressable catalyst for aqueous nitrate-to-ammonium electrocatalysis and demonstrate that catalytic selectivity is governed by the cooperative interplay between axial-ligand electronic tuning and local proton management. An isostructural series of lower-axial variants (C1–C4) was prepared by systematically modifying the native dimethylbenzimidazole environment, culminating in an l-histidine-ligated derivative (C4) bearing proximal −COOH/–NH2 functionality. In mildly acidic MOPS buffer (pH 5.81), C4 exhibited the highest performance, achieving ∼90% NH4+ Faradaic efficiency at −1.1 V vs SCE while effectively suppressing H2 and hydroxylamine formation compared with the other derivatives. Electrochemical studies reveal that axial-ligand engineering modulates the Co(III)/Co(I) redox manifold, facilitating access to the catalytically active Co(I) state and promoting nitrate activation. Mechanistic investigations support a pathway in which electrochemical reduction induces Co–CN bond dissociation and solvent coordination to generate a Co(I)-solvent intermediate, followed by nitrate binding and proton-coupled electron transfer through nitrite and hydroxylamine intermediates to ammonium. 15N isotopic labeling and in situ spectroelectrochemical measurements confirm the formation of nitrate-derived NH4+ and validate the proposed catalytic intermediates. To evaluate the transferability of this molecular design, the catalysts were immobilized on graphene oxide. The heterogeneous systems preserved the activity trend observed in solution, with C4@GO exhibiting the highest NH4+ selectivity, demonstrating that the electronic effects imparted by lower axial-ligand engineering remain operative after immobilization. Together, these results establish vitamin B12 as a versatile Co-corrin platform and identify axial-ligand-controlled electronic tuning coupled with spatially programmed proton delivery as a general strategy for designing efficient molecular and hybrid electrocatalysts for selective multiproton, multielectron nitrate reduction in water.

Interface-engineered Ni _0.5 Co _0.5 Fe ₂ O ₄ /LaFeO ₃ heterostructures exhibit enhanced interfacial coupling and magnetoelectric response, enabling multifunctional device applications.

Renewable energy-driven electrochemical CO2 reduction reaction (CO2RR) is reckoned as a potential pathway for establishing carbon-neutral chemical and fuel generation. Developing molecular complex-based heterogeneous electrocatalysts has emerged as a popular route for converting CO2 into specific C1 products, including CO, methanol, and formate. However, this approach has rarely culminated in the generation of a practically viable CO2 electrolyzer. In this work, a molecular Mn-carbonyl complex was designed with a specifically positioned multidentate triazole ligand scaffold. This complex was covalently anchored on graphene oxide (Mn-adpt@GO), which efficiently produced CO, HCOOH, and CH3OH from CO2 in aqueous media in an H-cell setup. The same Mn-adpt@GO material was deployed in an electrolyzer assembly to achieve ∼151 mA/cm2 current density with improved production of CH3OH during CO2RR over extended periods. This is a rare example of a heterogenized Mn-based molecular catalyst that facilitates the conversion of CO2 into CH3OH in an electrolyzer setup while retaining the molecular nature of the catalyst with appreciable stability. The in operando spectro-IR experiments indicated that this Mn-adpt@GO binds CO2 through the C-atom for the production of the major C1 products via the formation of a key surface-adsorbed COOH intermediate.

Developing potentially viable, cost-effective, and sustainable bifunctional electrocatalysts with promising activity toward the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in alkaline media.