Enhanced Photothermal Effect Assisted by Resonance Energy Transfer in Carbon/Covellite Core-Shell Nanoparticles toward a High-Performance Interfacial Water Evaporation Process.

Carbon and semiconductor nanoparticles are promising photothermal materials for various solar-driven applications. Inevitable recombination of photoinduced charge carriers in a single constituent, however, hinders the realization of a greater photothermal effect. Core-shell heterostructures utilizing the donor-acceptor pair concept with high-quality interfaces can inhibit energy loss from the radiation relaxation of excited species, thereby enhancing the photothermal effect. Here, core-shell structures composed of a covellite (CuS) shell (acceptor) and spherical carbon nanoparticle (CP) core (donor) (abbreviated as CP/CuS) are proposed to augment the photothermal conversion efficiency via the Förster resonance energy transfer (FRET) mechanism. The close proximity and spectral overlap of the donor and acceptor trigger the FRET mechanism, where the electronic excitation relaxation energy of the CP reinforces the plasmonic resonance and near-infrared absorption in CuS, resulting in boosting the overall photothermal conversion efficiency. CP/CuS core-shell coated on polyurethane (PU) foam exhibits a total solar absorption of 97.1%, leading to an elevation in surface temperature of 61.6 °C in dry conditions under simulated solar illumination at a power density of 1 kW m-2 (i.e., 1 sun). Leveraging the enhanced photothermal conversion emanated from the energy transfer effect in the core-shell structure, CP/CuS-coated PU foam achieves an evaporation rate of 1.62 kg m-2 h-1 and an energy efficiency of 93.8%. Thus, amplifying photothermal energy generation in core-shell structures via resonance energy transfer can be promising in solar energy-driven applications and thus merits further exploration.

Cobalt Sulfide/Nickel Sulfide Heterostructure Directly Grown on Nickel Foam: An Efficient and Durable Electrocatalyst for Overall Water Splitting Application.

Fabrication of high-performance noble-metal-free bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) in water is a promising strategy toward future carbon-neutral economy. Herein, a one-pot hydrothermal synthesis of cobalt sulfide/nickel sulfide heterostructure supported by nickel foam (CoS x/Ni3S2@NF) was performed. The Ni foam acted as the three-dimensional conducting substrate as well as the source of nickel for Ni3S2. The formation of CoS x/Ni3S2@NF was confirmed by X-ray diffraction and X-ray photoelectron spectroscopy. The formation of CoS x/Ni3S2@NF facilitated easy charge transport and showed synergistic electrocatalytic effect toward HER, OER, and overall water splitting in alkaline medium. Remarkably, CoS x/Ni3S2@NF showed catalytic activity comparable with that of benchmarking electrocatalysts Pt/C and RuO2. For CoS x/Ni3S2@NF, overpotentials of 204 and 280 mV were required to achieve current densities of 10 and 20 mA cm-2 for HER and OER, respectively, in 1.0 M KOH solution. A two-electrode system was formulated for overall water splitting reaction, which showed current densities of 10 and 50 mA cm-2 at 1.572 and 1.684 V, respectively. The prepared catalyst exhibited excellent durability in HER and OER catalyzing conditions and also in overall water splitting operation. Therefore, CoS x/Ni3S2@NF could be a promising noble-metal-free electrocatalyst for overall water splitting application.