Enhancing Surface Strain of Intermetallic Fuel Cell Catalysts by Composition-Induced Phase Transition.

The lattice parameter of platinum-based intermetallic compounds (IMCs), which correlates with the intrinsic activity of the oxygen reduction reaction (ORR), can be modulated by crystal phase engineering. However, the controlled preparation of IMCs with unconventional crystal structures remains highly challenging. Here, we demonstrate the synthesis of carbon-supported PtCu-based IMC catalysts with an unconventional L10 structure by a composition-regulated strategy. Experiment and machine learning reveal that the thermodynamically favorable structure changes from L11 to L10 when slight Cu atoms are substituted with Co. Benefiting from crystal-phase-induced strain enhancement, the prepared L10-type PtCu0.8Co0.2 catalyst exhibits much-enhanced mass and specific activities of 1.82 A mgPt-1 and 3.27 mA cmPt-2, which are 1.91 and 1.73 times higher than those of the L11-type PtCu catalyst, respectively. Our work highlights the important role of crystal phase in determining the surface strain of IMCs, and opens a promising avenue for the rational preparation of IMCs with different crystal phases by doping.

Reversible Electrochemical Gelation of Metal Chalcogenide Quantum Dots.

The ability to dictate the assembly of quantum dots (QDs) is critical for their integration into solid-state electronic and optoelectronic devices. However, assembly methods that enable efficient electronic communication between QDs, facilitate access to the reactive surface, and retain the native quantum confinement characteristics of the QD are lacking. Here we introduce a universal and facile electrochemical gelation method for assembling metal chalcogenide QDs (as demonstrated for CdS, ZnS, and CdSe) into macroscale 3-D connected pore-matter nanoarchitectures that remain quantum confined and in which each QD is accessible to the ambient. Because of the redox-active nature of the bonding between QD building blocks in the gel network, the electrogelation process is reversible. We further demonstrate the application of this electrogelation method for a one-step fabrication of CdS gel gas sensors, producing devices with exceptional performance for NO2 gas sensing at room temperature, thereby enabling the development of low-cost, sensitive, and reliable devices for air quality monitoring.

Machine-learning-accelerated design of high-performance platinum intermetallic nanoparticle fuel cell catalysts.

Carbon supported PtCo intermetallic alloys are known to be one of the most promising candidates as low-platinum oxygen reduction reaction electrocatalysts for proton-exchange-membrane fuel cells. Nevertheless, the intrinsic trade-off between particle size and ordering degree of PtCo makes it challenging to simultaneously achieve a high specific activity and a large active surface area. Here, by machine-learning-accelerated screenings from the immense configuration space, we are able to statistically quantify the impact of chemical ordering on thermodynamic stability. We find that introducing of Cu/Ni into PtCo can provide additional stabilization energy by inducing Co-Cu/Ni disorder, thus facilitating the ordering process and achieveing an improved tradeoff between specific activity and active surface area. Guided by the theoretical prediction, the small sized and highly ordered ternary Pt2CoCu and Pt2CoNi catalysts are experimentally prepared, showing a large electrochemically active surface area of ~90 m2 gPt‒1 and a high specific activity of ~3.5 mA cm‒2.

Symmetry-Breaking p-Block Antimony Single Atoms Trigger N-Bridged Titanium Sites for Electrocatalytic Nitrogen Reduction with High Efficiency.

The electrochemical nitrogen reduction reaction (eNRR) under mild conditions emerges as a promising approach to produce ammonia (NH3) compared to the typical Haber-Bosch process. Herein, we design an asymmetrically coordinated p-block antimony single-atom catalyst immobilized on nitrogen-doped Ti3C2Tx (Sb SA/N-Ti3C2Tx) for eNRR, which exhibits ultrahigh NH3 yield (108.3 µg h-1 mgcat-1) and excellent Faradaic efficiency (41.2%) at -0.3 V vs RHE. Complementary in situ spectroscopies with theoretical calculations reveal that the nitrogen-bridged two titanium atoms triggered by an adjacent asymmetrical Sb-N1C2 moiety act as the active sites for facilitating the protonation of the rate-determining step from *N2 to *N2H and the kinetic conversion of key intermediates during eNRR. Moreover, the introduction of Sb-N1C2 promotes the formation of oxygen vacancies to expose more titanium sites. This work presents a strategy for single-atom-decorated ultrathin two-dimensional materials with the aim of simultaneously enhancing NH3 yield and Faradaic efficiency for electrocatalytic nitrogen reduction.