In this study, pristine MnO₂ catalyst was synthesized by hydrothermal technique and annealed at 400 and 600°C (MnO₂@400°C and MnO₂@600°C) transforming it into nanorods in a nitrogen atmosphere. The heat treatment process ameliorates the catalytic activity of the MnO₂ catalyst by inducing oxygen vacancies. The catalyst is characterized by scanning electron microscope, and X‐ray diffraction, Fourier transforms infrared spectroscopy (FTIR), Electron paramagnetic resonance (EPR), and X‐ray Photoelectron Spectroscopy, whereas the oxygen reduction reaction (ORR) activity examined through rotating disc electrode and fuel cell test station. To elucidate the effect of sintering temperature on the MnO₂ nanorods, the high angle annular dark‐field (HAADF) imaging was carried out on the samples. MnO₂@400°C showed preeminent robustness to withstand austere alkaline environment during the experiment and possessed high electrocatalytic activity for the ORR with current density and onset potential values of 6.4 mA cm^–2 and 0.80 V VS (RHE), respectively. The single‐cell test experiment of alkaline fuel cell delivered peak power density 81 mW/cm at 50°C. It is believed that this idiosyncratic behavior of MnO₂ nanorods is due to the preferential growth on (211) and (310) indices and coexistence of optimized Mn⁴⁺/Mn³⁺ oxidation states as well as the creation of optimum oxygen vacancies on MnO₂ nanorods. Moreover, the stretching of MnO₂ nanorods occurs with increasing temperature and thus increasing the surface area to volume ratio. Thus thermal treatment shows that MnO₂ is highly sensitive toward temperature variation and optimum ORR results can be obtained at adequate temperatures.

We report a robust two-step method for developing adherent and anticorrosive molybdenum (Mo)-based coatings over an aluminum (Al) 6061 alloy substrate using a femtosecond (fs) laser. The fs laser nanostructuring of Al 6061 alloy in air gives rise to regular arrays of microgrooves exhibiting superhydrophilic surface properties. The microstructured surface is further coated with an Mo layer using the fs-pulsed laser deposition (fs-PLD) technique. The combination of the two femtosecond laser surface treatments (microstructuring followed by coating) enabled the development of a highly corrosion-resistant surface, with a corrosion current of magnitude less than that of the pristine, the only structured, and the annealed alloy samples. The underlying mechanism is attributed to the laser-assisted formation of highly rough hierarchical oxide structures on the Al 6061 surface along with post heat treatment, which passivates the surface and provide the necessary platform for firm adhesion for Mo coating. Our results reveal that the corrosive nature of the Al-based alloys can be controlled and improved using a combined approach of femtosecond laser-based surface structuring and coating.

In this study, the electrocatalytic properties of single-phase face-centered cubic high entropy alloy electrodes with equiatomic compositions of CoNiFeCr, CoNiFeV, and CoNiFe(Cr/V) are explored for the hydrogen evolution reaction (HER) in 1M KOH and 0.5M H2SO4. Among these, the CoNiFe(Cr/V) High Entropy Alloy (HEA) electrodes exhibited superior performance, achieving overpotentials of 277 and 45 mV (vs reference hydrogen electrode) at 10 mA/cm2 in alkaline and acidic media, respectively, surpassing their counterparts and approaching the efficiency of commercial Raney-Ni and Pt/C catalysts. Long-term stability tests, including steady state chronoamperometry and potentiodynamic cyclic voltammetry, revealed remarkable corrosion resistance in both environments. The catalytic activity was significantly enhanced by the inclusion of Cr and V. These oxyphilic elements, with their larger atomic radii, induce a heterogeneous surface charge distribution that enhances the electrocatalytic performance of the CoNiFe(Cr/V) HEA. This work highlights a promising candidate for HER applications and sets the stage for a broader exploration of high entropy alloys in advanced catalytic systems.

CoNiCr is a prototypical example of topical multi-principle element alloys with superior cryogenic and high-temperature mechanical strength, corrosion, oxidation resistance, and yet-to-be-explored magnetic and electronic functionalities. The remarkable properties of this transition metal ternary system are not only due to atomic radii, electronic configurational mismatch, and atomic volume misfit but are also dependent on the debated magnetically driven chemical short-range order. The current study focuses on the electric and magnetic properties of the single-phase face-centered cubic CoNi(Cr/V) system in which V is introduced to the system at the expense of Cr to fine-tune the volume misfit in the system. All the samples exhibited ultra-small magnetic moments due to the complex magnetic interactions of the constituent elements. The electric transport measurements revealed a strange metallicity evidenced through the observation of the linear temperature dependence of the resistivity. Our findings support the recent theoretical studies on the magnetically driven chemical short-range order of the CoNiCr system.

A two-step femtosecond-pulsed laser deposition (fs-PLD) process is reported for the rapid development of uniform, poreless, crack-free, and well-adhering amorphous coatings of source materials with a high melting point. The first step comprises a high-rate raw deposition of the source material via fs-PLD, followed by a second step of scanning the raw sample with fs laser pulses of optimized fluence and scan parameters. The technique is applied to develop substoichiometric molybdenum oxide (MoO_x, x < 3) coatings on mild steel. The thickness of the layer was ~4.25 μm with roughness around 0.27 μm. Comprehensive surface characterization reveals highly uniform and relatively moderate roughness coatings, implying the potential of these films as robust corrosion-resistant coats. Corrosion measurements in an aqueous NaCl environment revealed that the coated mild steel samples possess an average corrosion inhibition efficiency of around 95% relative to polished mild steel.