Defect engineering is an effective strategy to improve the activity of two-dimensional molybdenum disulfide base planes toward electrocatalytic hydrogen evolution reaction. Here, we report a Frenkel-defected monolayer MoS2 catalyst, in which a fraction of Mo atoms in MoS2 spontaneously leave their places in the lattice, creating vacancies and becoming interstitials by lodging in nearby locations. Unique charge distributions are introduced in the MoS2 surface planes, and those interstitial Mo atoms are more conducive to H adsorption, thus greatly promoting the HER activity of monolayer MoS2 base planes. At the current density of 10 mA cm−2, the optimal Frenkel-defected monolayer MoS2 exhibits a lower overpotential (164 mV) than either pristine monolayer MoS2 surface plane (358 mV) or Pt-single-atom doped MoS2 (211 mV). This work provides insights into the structure-property relationship of point-defected MoS2 and highlights the advantages of Frenkel defects in tuning the catalytic performance of MoS2 materials.

A facile method to make optoelectronic devices formed from organic thin-film transistors that are functionalized by photochromic spiropyran dyes in a nondestructive manner has been developed. When PDMS stamps are employed, alkane-containing spiropyran molecules can be coated simply onto the surface of organic thin films in a noninvasive manner. Upon UV irradiation, the molecules undergo isomerization from the neutral closed form to the charge-separated merocyanine form, producing the local electrostatic environment. This photoinduced electrostatic environment can function as a local negative gate voltage, thus increasing the electrical conductivity in p-type devices and decreasing the electrical conductivity in n-type devices. Further irradiation with visible light or keeping the devices in the dark can switch the device conductance back to their initial value. This method is reversible and reproducible on different devices with different thickness over a long period of time.

Point defects of heteroatoms and vacancies can activate the inert basal plane of molybdenum sulfide (MoS2) to improve its performance on catalyzing the hydrogen evolution reaction (HER). However, the synergy between heteroatoms and vacancies is still unclear. Here, a chemical vapor deposition‐assisted in situ vanadium (V) doping method is used to synthesize monolayer MoS2 with abundant and tunable vacancies and V‐dopants in the lattice. Ten delicate defect configurations are prepared to provide a complex system for the relationship investigation between microstructure and catalytic performance. The combination of on‐chip electrochemical tests and theoretical calculations indicates that the HER performance greatly depends on the type and amount of defect configurations. The optimal configuration is that three V atoms are aggregated and accompanied by abundant sulfur vacancies, in which, H atoms directly interact with Mo and V atoms to form the most stable metal‐bridge structure. The on‐chip measurements also confirm that the sample with high concentrations of this type of defect configuration exhibits the best catalytic performance, indicating the efficient synergy in the optimal configuration. The revealed effects of defect configurations are expected to inspire the design and regulation of high‐efficiency 2D catalysts.