Graphene (G) films were grown on copper foils by chemical vapor deposition and transferred onto n-type silicon (Si) to form G/Si Schottky heterojunction solar cells. The power conversion efficiencies (PCEs) of the G/Si solar cells were in the range of 1.94-2.66%. Four volatile oxidants HNO 3 , HCl, H 2 O 2 and SOCl 2 were employed to treat the graphene films in the G/Si solar cells, and the PCEs could be greatly enhanced after being treated by all the volatile oxidants and SOCl 2 doping showed the best improvement. A solar cell with an initial PCE of 2.45% could be increased to 5.95% upon SOCl 2 doping treatment. The PCE stability of the volatile oxidant-treated cells was also investigated. The PCEs decreased with time, while SOCl 2 and HCl showed much better PCE stability than HNO 3 and H 2 O 2 .

The coronavirus disease outbreak of 2019 has been causing significant loss of life and unprecedented economic loss throughout the world. Social distancing and face masks are widely recommended around the globe to protect others and prevent the spread of the virus through breathing, coughing, and sneezing. To expand the scientific underpinnings of such recommendations, we carry out high-fidelity computational fluid dynamics simulations of unprecedented resolution and realism to elucidate the underlying physics of saliva particulate transport during human cough with and without facial masks. Our simulations (a) are carried out under both a stagnant ambient flow (indoor) and a mild unidirectional breeze (outdoor), (b) incorporate the effect of human anatomy on the flow, (c) account for both medical and non-medical grade masks, and (d) consider a wide spectrum of particulate sizes, ranging from 10 µm to 300 µm. We show that during indoor coughing some saliva particulates could travel up to 0.48 m, 0.73 m, and 2.62 m for the cases with medical grade, non-medical grade, and without facial masks, respectively. Thus, in indoor environments, either medical or non-medical grade facial masks can successfully limit the spreading of saliva particulates to others. Under outdoor conditions with a unidirectional mild breeze, however, leakage flow through the mask can cause saliva particulates to be entrained into the energetic shear layers around the body and transported very fast at large distances by the turbulent flow, thus limiting the effectiveness of facial masks.

MoS2-based electrocatalysts are promising cost-effective replacements for Pt-based catalysts for hydrogen evolution by water splitting, yet achieving high current density at low overpotential remains a challenge. Herein, a binder-free electrode of MoS2/CNF (carbon nanofiber) is prepared by electrospinning and subsequent thermal treatment. The growth of MoS2 nanoplates contained within or protruding out from the CNF can be controlled by adding urea or ammonium bicarbonate to the electrospinning precursors, due to the cross-linking effects of urea and the increased porosity caused by pyrolysis of ammonium bicarbonate allowing growth through pores in the CNF. By virtue of the abundant exposed edges in this microstructure and strong bonding between the catalyst and the conductive carbon network, the composite material exhibits ultrahigh electrocatalytic hydrogen evolution activity in acidic solutions, with current densities of 500 and 1000 mA/cm2 at overpotentials of 380 and 450 mV, respectively, exceeding the performance of many reported MoS2-based catalysts and even commercial Pt/C catalysts. Thus, MoS2/CNF membranes show potential as efficient and flexible binder-free electrodes for electrocatalytic hydrogen production.

Large-area (e.g. centimeter size) graphene sheets are usually synthesized via pyrolysis of gaseous carbon precursors (e.g. methane) on metal substrates like Cu using chemical vapor deposition (CVD), but the presence of grain boundaries and the residual polymers during transfer deteriorates significantly the properties of the CVD graphene. If carbon nanotubes (CNTs) can be covalently bonded to graphene, the hybrid system could possess excellent electrical conductivity, transparency and mechanical strength. In this work, conducting and transparent CNT-graphene hybrid films were synthesized by a facile solid precursor pyrolysis method. Furthermore, the synthesized CNT-graphene hybrid films display enhanced photovoltaic conversion efficiency when compared to devices based on CNT membranes or graphene sheets. Upon chemical doping, the graphene-CNT/Si solar cells reveal power conversion efficiencies up to 8.50%.