Electrochemically converting nitrate, a widespread water pollutant, back to valuable ammonia is a green and delocalized route for ammonia synthesis, and can be an appealing and supplementary alternative to the Haber-Bosch process. However, as there are other nitrate reduction pathways present, selectively guiding the reaction pathway towards ammonia is currently challenged by the lack of efficient catalysts. Here we report a selective and active nitrate reduction to ammonia on Fe single atom catalyst, with a maximal ammonia Faradaic efficiency of ~ 75% and a yield rate of up to ~ 20,000 μg h−1 mgcat.−1 (0.46 mmol h−1 cm−2). Our Fe single atom catalyst can effectively prevent the N-N coupling step required for N2 due to the lack of neighboring metal sites, promoting ammonia product selectivity. Density functional theory calculations reveal the reaction mechanisms and the potential limiting steps for nitrate reduction on atomically dispersed Fe sites.

Highly active, stable, and cheap Pt-free catalysts for the hydrogen evolution reaction (HER) are facing increasing demand as a result of their potential use in future energy-conversion systems. However, the development of HER electrocatalysts with Pt-like or even superior activity, in particular ones that can function under alkaline conditions, remains a significant challenge. Here, the synthesis of a novel carbon-loaded ruthenium nanoparticle electrocatalyst (Ru@CQDs) for the HER, using carbon quantum dots (CQDs), is reported. Electrochemical tests reveal that, even under extremely alkaline conditions (1 m KOH), the as-formed Ru@CQDs exhibits excellent catalytic behavior with an onset overpotential of 0 mV, a Tafel slope of 47 mV decade , and good durability. Most importantly, it only requires an overpotential of 10 mV to achieve the current density of 10 mA cm . Such catalytic characteristics are superior to the current commercial Pt/C and most noble metals, non-noble metals, and nonmetallic catalysts under basic conditions. These findings open a new field for the application of CQDs and add to the growing family of metal@CQDs with high HER performance.

Cesium-based trihalide perovskites have been demonstrated as promising light absorbers for photovoltaic applications due to their superb composition stability. However, the large energy losses (E ) observed in inorganic perovskite solar cells has become a major hindrance impairing the ultimate efficiency. Here, an effective and reproducible method of modifying the interface between a CsPbI Br absorber and polythiophene hole-acceptor to minimize the E is reported. It is demonstrated that polythiophene, deposited on the top of CsPbI Br, can significantly reduce electron-hole recombination within the perovskite, which is due to the electronic passivation of surface defect states. In addition, the interfacial properties are improved by a simple annealing process, leading to significantly reduced energy disorder in polythiophene and enhanced hole-injection into the hole-acceptor. Consequently, one of the highest power conversion efficiency (PCE) of 12.02% from a reverse scan in inorganic mixed-halide perovskite solar cells is obtained. Modifying the perovskite films with annealing polythiophene enables an open-circuit voltage (V ) of up to 1.32 V and E of down to 0.5 eV, which both are the optimal values reported among cesium-lead mixed-halide perovskite solar cells to date. This method provides a new route to further improve the efficiency of perovskite solar cells by minimizing the E .

Piezochromic materials, which show color changes resulting from mechanical grinding or external pressure, can be used as mechanosensors, indicators of mechano-history, security papers, optoelectronic devices, and data storage systems. A class of piezochromic materials with unprecedented two-photon absorptive and yellow emissive carbon dots (CDs) was developed for the first time. Applied pressure from 0-22.84 GPa caused a noticeable color change in the luminescence of yellow emissive CDs, shifting from yellow (557 nm) to blue-green (491 nm). Moreover, first-principles calculations support transformation of the sp domains into sp -hybridized domains under high pressure. The structured CDs generated were captured by quenching the high-pressure phase to ambient conditions, thus greatly increasing the choice of materials available for a variety of applications.

A recently created class of inorganic 2D materials, MXenes, has become a subject of intensive research. Reducing their dimensionality from 2D to 0D quantum dots (QDs) could result in extremely useful properties and functions. However, this type of research is scarce, and the reported Ti 3 C 2 MXene QDs (MQDs) have only shown blue fluorescence emission. This work demonstrates a facile, high‐output method for preparing bright white emitting Ti 3 C 2 MQDs. The resulting product is two layers thick with a lateral dimension of 13.1 nm. Importantly, the as prepared Ti 3 C 2 MQDs present strong two‐photon white fluorescence. Their fluorescence under high pressure is also investigated and it is found that the white emission is very stable and the pressure makes it possible to change from cool white emission to warm white emission. Hybrid nanocomposites are then fabricated by polymerizing Ti 3 C 2 MQDs in polydimethylsiloxane (PDMS) solution, and the bright white emitting hybrid materials in white light‐emitting diodes are used. This work provides a facile and general approach to modulate various nanoscale MXene materials, and could further aid the wide development of applications for MXene materials in various optical‐related fields.

The conductivity enhancement in solvent treated PEDOT:PSS is a result of the solvation of the PSS shell, leading to the release of conductive PEDOT in the core.

Carbon dots (CDs) have excellent luminescence characteristics, such as good light stability, high quantum yield (QY), long phosphorescence lifetime, and a wide emission wavelength range, resulting in CDs’ great success in optical applications. Understanding the structure–property relationships in CDs is essential for their use in optoelectronic applications. However, because of the complex nature of CD structures and synthesis processes, understanding the luminescence mechanism and structure–property relationships of CDs is a big challenge. This Perspective reviews the theoretical efforts toward the understanding of structure–property relationships and discusses the challenges that need to be overcome in future development of CDs.

Carbonized polymer dots (CPDs) have great potential for bioimaging and biosensing owing to their low toxicity, low cost, resistance to photobleaching, and low environmental impact. Here, the hydrothermal condensation of biomolecules (l‐serine and l‐tryptophan) is used to vary the CPDs' inner structure from amorphous to lattice. A new type of carbon lattice CPD is thus demonstrated that is bright (the photoluminescence quantum yield (PLQY) is as high as 89.57%) and shows room‐temperature ferromagnetism (RTFM), with the magnetic moment increasing from 0.0025 emu g−1 in crosslinked polymer clusters to 0.021 emu g−1 in the latticed sample. Hydrothermal synthesis at 300 °C leads to a distinct type of CPD with an obvious carbon lattice, which shows the highest PLQY and the greatest ferromagnetism. Then, the origin of the RTFM is examined in the CPDs via first‐principles calculation, revealing that graphitic nitrogen triggers RTFM in CPDs. Moreover, a possible growth mechanism is suggested that includes kinetics as an important factor in the formation of the CPD crystallites. Overall, these findings identify graphitic nitrogen and high crystallinity as crucial to the enhancement of the CPDs' photoluminescence and room‐temperature ferromagnetism which suggests that they deserve more research attention to develop practical applications.