The conformal integration of electronic systems with irregular, soft objects is essential for many emerging technologies. We report the design of van der Waals thin films consisting of staggered two-dimensional nanosheets with bond-free van der Waals interfaces. The films feature sliding and rotation degrees of freedom among the staggered nanosheets to ensure mechanical stretchability and malleability, as well as a percolating network of nanochannels to endow permeability and breathability. With an excellent mechanical match to soft biological tissues, the freestanding films can naturally adapt to local surface topographies and seamlessly merge with living organisms with highly conformal interfaces, rendering living organisms with electronic functions, including leaf-gate and skin-gate transistors. On-skin transistors allow high-fidelity monitoring and local amplification of skin potentials and electrophysiological signals.

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Proton exchange membrane fuel cells (PEMFCs) offer an attractive zero-emission mobile power source. However, the requirement of excessive platinum group metal (PGM) catalysts to facilitate the sluggish oxygen reduction reaction (ORR) in PEMFCs has prevented their widespread adoption. Despite tremendous progress in catalyst development with greatly increased catalytic activities, the reduction of PGM loading in practical PEMFCs remains a challenge. The ORR in PEMFCs occurs at a catalyst-electrolyte-gas three-phase interface, with multi-faceted challenges involving the activity of the catalysts, available active sites, and concerted transport of the reactants (oxygen, protons) to and removal of the product (water) from the active sites. The reduction of PGM loading reduces the number of catalytic sites, requiring a higher reaction rate on each site to sustain the overall power output, which in turn necessitates faster delivery of the reactants to and removal of the products from each active site. A desirable interface must allow efficiently feeding oxygen and protons to the catalytic sites without starving the reaction and must allow timely removal of water to avoid interface flooding. Herein we report the design of the three-phase microenvironment in PEFMCs by tailoring the interactions between the carbon supports and the electrolyte ionomers. We show that the carbon surface with 2.4% oxygen interacts with the ionomers through both its hydrophilic and hydrophobic regions, creating favorable transport paths for rapid delivery of both oxygen and protons, and timely removal of water. Such an elaborated interfacial design allows reducing costly platinum catalysts while maintaining state-of-the-art performance. For the first time we demonstrate PEMFCs with all key ORR catalyst performance metrics, including mass activity, rated power and durability, surpassing the U.S. DOE targets.

Systematic control of grain boundary densities in various platinum (Pt) nanostructures was achieved by specific peptide-assisted assembly and coagulation of nanocrystals. A positive quadratic correlation was observed between the oxygen reduction reaction (ORR) specific activities of the Pt nanostructures and the grain boundary densities on their surfaces. Compared to commercial Pt/C, the grain-boundary-rich strain-free Pt ultrathin nanoplates demonstrated a 15.5 times higher specific activity and a 13.7 times higher mass activity. Simulation studies suggested that the specific activity of ORR was proportional to the resident number and the resident time of oxygen on the catalyst surface, both of which correlate positively with grain boundary density, leading to improved ORR activities.

MoS2 has emerged as a good application prospect in the electrocatalytic hydrogen evolution reaction (HER). Nevertheless, the catalytic activity of MoS2 is greatly restricted by its inferior electrical conductivity, inadequate exposure of active edge sites, and sluggish water dissociation dynamics. Herein, a 1D/2D heteronanostructure composed of SiC nanowires wrapped with MoS2 nanosheets was prepared via the hydrothermal synthesis of MoS2 on highly connected SiC nanowires (SiCnw). The nanocomposites exhibit an emerging tectorum-like morphology with interface connections of C–Mo bonds, which benefit the efficient interfacial transmission of electrons. Due to the synergetic catalytic effects of MoS2 nanosheets and SiC nanowires, the MoS2/SiCnw nanocomposites possess efficient catalytic performance with a low Tafel slope (55 mV/dec). SiC nanocrystals could reduce the activated water dissociation energy barrier, and the morphologies of connected nanowires could improve the active site exposure and charge transport. The nanocomposites possess favorable hydrogen adsorption free energy from density functional theory (DFT) calculations. The electrocatalytic performance of MoS2/SiCnw nanocomposites could be further improved by assembling the nanocomposites on a carbon fiber paper to enhance the electronic transmission efficiency.