For the first time, we demonstrated
that transition metal and nitrogen codoped carbon nanocomposites synthesized
by pyrolysis and heat treatment showed excellent catalytic activity
toward hydrogen evolution reaction (HER) in both acidic and alkaline
media. The overpotential at 10 mA cm–2 was 235 mV
in a 0.5 M H2SO4 solution at a catalyst loading
of 0.765 mg cm–2 for Co–N–C. In a
1 M KOH solution, the overpotential was only slightly increased by
35 mV. The high activity and excellent durability (negligible loss
after 1000 cycles in both acidic and alkaline media) make this carbon-based
catalyst a promising alternative to noble metals for HER. Electrochemical
and density functional theory (DFT) calculation results suggested
that transition metals and nitrogen played a critical role in activity
enhancement. The active sites for HER might be associated with metal/N/C
moieties, which have been also proposed as reaction centers for oxygen
reduction reaction.
A microsecond time-scale photonic lift-off (PLO) process was used to fabricate mechanically flexible photovoltaic devices (PVs) with a total thickness of less than 20 μm. PLO is a rapid, scalable photothermal technique for processing extremely thin, mechanically flexible electronic and optoelectronic devices. PLO is also compatible with large-area devices, roll-to-roll processing, and substrates with low temperature compatibility. As a proof of concept, PVs were fabricated using CuInSe 2 nanocrystal ink deposited at room temperature under ambient conditions on thin, plastic substrates heated to 100 °C. It was necessary to prevent cracking of the brittle top contact layer of indium tin oxide (ITO) during lift-off, either by using a layer of silver nanowires (AgNW) as the top contact or by infusing the ITO layer with AgNW. This approach could generally be used to improve the mechanical versatility of current collectors in a variety of ultrathin electronic and optoelectronic devices requiring a transparent conductive contact layer.
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