Since the preceding decade, strain engineering has been playing a vital role in modifying the activity of electrocatalysts. Incorporation of tensile strain into a Pd-based system usually requires substitution with larger atoms (usually a third row expensive transition metals). This work provides a unique strategy of introducing tensile strain by the substitution of small and low cost copper atoms (inverse strain effect) at the palladium sites of Pd 17 Se 15 . The Pd atom being in the +2 oxidation state adsorbs hydrogen very weakly, and Se, in its elemental state, binds weakly to H* adsorbate. However, the presence of Pd modulates the electronic structure of Se to have ΔG H* close to 0 and favors the progress of the reaction. Cu substitution further lowers ΔG H* , thus favoring the reaction. This unique synergistic effect between the two processes is accountable for better activity, high stability of 30 000 cycles and significantly high turnover frequency of 126.3 s −1 for (CuPd) 17 Se 15 .

We report facile preparation of water dispersible CuS quantum dots (2–4 nm) and nanoparticles (5–11 nm) through a nontoxic, green, one-pot synthesis method. Optical and microstructural studies indicate the presence of surface states and defects (dislocations, stacking faults, and twins) in the quantum dots. The smaller crystallite size and quantum dot formation have significant effects on the high energy excitonic and low energy plasmonic absorption bands. Effective two-photon absorption coefficients measured using 100 fs laser pulses employing open-aperture Z-scan in the plasmonic region of 800 nm reveal that CuS quantum dots are better ultrafast optical limiters compared to CuS nanoparticles.

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The use of hydrogen, being an environmentally cleaner source of energy, may reduce the pressing problem of CO 2 emissions due to the burning of conventional fossil fuels. However, the prolonged production of hydrogen is a major issue and can be solved through designing a stable electrocatalyst. In this work, we have designed a Ni-doped Pd 17 Se 15 catalyst that retains its activity for 20000 electrochemical cycles. The enhanced stability of this electrocatalyst can be attributed to the reversal of the activity center from the Pd to the Se center through Ni substitution. The concept of activating the chalcogen center and deactivating the Pd site is supported through theoretical calculations. This work provides a unique strategy of tuning catalysts toward higher activity and stability.

Toward the need for solid-state fluorescent quantum dots, resistant to self-quenching, we describe a solvothermal-assisted sol–gel method to synthesize Se quantum dots. Morphological and crystalline characterizations reveal that Se quantum dots (average size 3–8 nm) have a trigonal crystal structure. The presence of planar defects (dislocations, stacking faults, twins, and grain boundaries) suggests formation of Se nanocrystallites through aggregation-based crystal growth mechanisms. Under ultraviolet excitation, the quantum dots exhibit an excitation wavelength-dependent solid-state blue emission with an average lifetime of 1.96 ns. Depending on fluorescence quenching by curcumin, selenium quantum dots act as ideal candidates for inner filter effect-based curcumin sensing.

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We report a cubic to amorphous transformation of selenium in silica xerogel with potential industrial application as ultrafast laser safety materials.

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