MoS 2 -based transition-metal chalcogenides are considered as cost-effective, highly active, and stable materials with great potential in the application of electrocatalytic hydrogen production. However, their limited quantity of active sites and poor conductivity have hampered the efficiency of hydrogen production. Combining calculations and experiments, we demonstrate that P dopants could be the new active sites in the basal plane of MoS 2 and help improve the intrinsic electronic conductivity, leading to a significantly improved activity for hydrogen evolution. Furthermore, the P-doped MoS 2 nanosheets show enlarged interlayer spacing, facilitating hydrogen adsorption and release progress. Experimental results indicate that the P-doped MoS 2 nanosheets with enlarged interlayer spacing exhibit remarkable electrocatalytic activity and good long-term operational stability (with Tafel slope of 34 mV/dec and an extremely low overpotential of ∼43 mV at 10 mA/cm 2 ) . Our method demonstrated a facile technology for improving the electrocatalytic efficiency of MoS 2 for hydrogen evolution reaction through nonmetal doping, which could be explored to enhance and understand the catalytic properties of other transition-metal chalcogenides.

We demonstrate the alignment-preserving transfer of parallel graphene nanoribbons (GNRs) onto insulating substrates. The photophysics of such samples is characterized by polarized Raman and photoluminescence (PL) spectroscopies. The Raman scattered light and the PL are polarized along the GNR axis. The Raman cross section as a function of excitation energy has distinct excitonic peaks associated with transitions between the one-dimensional parabolic subbands. We find that the PL of GNRs is intrinsically low but can be strongly enhanced by blue laser irradiation in ambient conditions or hydrogenation in ultrahigh vacuum. These functionalization routes cause the formation of sp defects in GNRs. We demonstrate the laser writing of luminescent patterns in GNR films for maskless lithography by the controlled generation of defects. Our findings set the stage for further exploration of the optical properties of GNRs on insulating substrates and in device geometries.

The development of high-energy and high-power density supercapacitors (SCs) is critical for enabling next-generation energy storage applications. Nanocarbons are excellent SC electrode materials due to their economic viability, high-surface area, and high stability.Although nanocarbons have high theoretical surface area and hence high double layer capacitance, the net amount of energy stored in nanocarbon-SCs is much below theoretical limits due to two inherent bottlenecks: i) their low quantum capacitance and ii) limited ionaccessible surface area. Here, we demonstrate that defects in graphene could be effectively used to mitigate these bottlenecks by drastically increasing the quantum capacitance and opening new channels to facilitate ion diffusion in otherwise closed interlayer spaces. Our results support the emergence of a new energy paradigm in SCs with 250% enhancement in double layer capacitance beyond the theoretical limit.Furthermore, we demonstrate prototype defect engineered bulk SC devices with energy densities 500% higher than state-of-the-art commercial SCs without compromising the power density. IntroductionSupercapacitors (SCs) are novel electrochemical devices that store energy through reversible adsorption of ionic species from an electrolyte on highly porous electrode surfaces. SCs are highly durable (lifetime >10,000 cycles) with power densities (10 kW/kg) that are an order of magnitude larger than batteries. But the low energy density (10 Wh/kg) of SCs 1 relative to batteries precludes their use in practical applications despite their ability to withstand >10,000 cycles. Graphene-based nanocarbons are ideal electrode materials for SCs due to their low cost, high stability, and high specific surface area. Indeed, an outstanding characteristic of single-layer graphene is its high specific surface area ~2675 m 2 /g, which sets an upper limit for electrical double layer capacitance (C dl ) ~21 µF/cm 2 (~550 F/g). 1-4 Notwithstanding this theoretical limit, there are two intrinsic bottlenecks that are impeding the emergence of high energy density SC devices:i) typically only 50-70% of the theoretical surface area is accessible to ionic species from the electrolyte, which limits the overall capacitance (10-15 µF/cm 2 ) and leads to low energy density, and ii) although the total energy that can be harnessed from a SC device depends predominantly on ion-accessible surface area, it is not the only factor. The presence of the so-called small quantum capacitance (C Q ) in series for nanocarbon electrodes, arising from their low electronic density of states at the Fermi level (DOS(E F )), overwhelms the high C dl further reducing the already limited capacitance and low energy density. 5-7While the efforts to increase energy density have been focused either on increasing the active surface area or the addition of pseudo-capacitance through redox active materials, there is a clear lack of methodologies to simultaneously address the inherent challenges described above. Here, we experimentally show that eng...

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