Competition-Induced Macroscopic Superlubricity of Ionic Liquid Analogues by Hydroxyl Ligands Revealed by in Situ Raman

High load-bearing capacity is one of the crucial indicators for liquid superlubricants to move toward practicality. However, some of the current emerging systems not only have low contact pressures but also are highly susceptible to further degradation due to water adsorption and even superlubricity failure. Herein, a novel choline chloride-based ionic liquid analogues (ILAs) of a superlubricant with triethanolamine (TEOA) as the H-bond donor is reported for the first time; it obtains an ultralow coefficient of friction (0.005) and high load-bearing capacity (360 MPa, more than 2 times that of similar systems) due to adsorption of a small amount of water (<5 wt %) from the air. In situ Raman combined with 1H NMR and FTIR techniques reveals that adsorbed water competes with the hydroxyl group of TEOA for coordination with Cl–, leading to the conversion of some strong H-bonds to weak H-bonds in ILAs; the localized strong H-bonds and weak H-bonds endow the ILAs with high load-bearing capacity and the formation of ultralow shear-resistance sliding interfaces, respectively, under the shear motion. This study proposes a strategy to modulate the interactions between liquid species using adsorbed water from air as a competing ligand, which provides new insights into the design of ILA-based macroscopic liquid superlubricants with a high load-bearing capacity

Alloyed Co–Mo Nitride as High-Performance Electrocatalyst for Oxygen Reduction in Acidic Medium

Exploring cheap and stable electrocatalysts to replace Pt for the oxygen reduction reaction (ORR) is now the key issue for the large-scale application of fuel cells. Herein, we report an alloyed Co–Mo nitride electrocatalyst supported on nitrogen-doped carbon nanocages (NCNCs) which combines the merits of cobalt nitride and molybdenum nitride, showing high activity comparable to that of cobalt nitride and progressively enhanced stability with the increase in the Mo ratio. The typical Co_0.5Mo_0.5N_<i>y</i>/NCNCs catalyst demonstrates excellent ORR performance in acidic medium with a high onset potential of 808 mV vs RHE, superior stability (>80% retention after 100 h of continuous testing in 0.5 mol L^–1 H₂SO₄), a dominant four-electron catalytic process, and good immunity to methanol crossover. Together with the convenient and scalable preparation as well as the low cost, the alloyed Co–Mo nitride electrocatalyst shows great potential in application for fuel cells. This study also suggests a promising strategy to develop non-precious-metal ORR electrocatalysts in acidic medium: i.e., to construct the alloyed compounds by combining substances with respective high activity and high stability

Alcohol-Tolerant Platinum Electrocatalyst for Oxygen Reduction by Encapsulating Platinum Nanoparticles inside Nitrogen-Doped Carbon Nanocages

Pt-based electrocatalysts are the most popular for direct alcohol fuel cells, but their performances easily deteriorate for the oxygen reduction reaction (ORR) at the cathode because of the alcohol crossover effect. Herein, we report the novel Pt electrocatalyst encapsulated inside nitrogen-doped carbon nanocages (Pt@NCNC), which presents excellent alcohol-tolerant ORR activity and durability in acidic media, far superior to the Pt counterpart immobilized outside the nanocages (Pt/NCNC). The superb performance is correlated with the molecule-sieving effect of the micropores penetrating through the shells of the nanocages, which admit the small-sized oxygen and ions but block the large-sized alcohols into the nanocages. This mechanism is confirmed by examining the size dependence of ORR and alcohol oxidation activities by regulating the micropores sizes. This study provides a promising strategy to develop the superior alcohol-tolerant Pt-based ORR electrocatalyst in acidic media