Distributions of Hydrochloric Acid between Water and Organic Solutions of Tri‑<i>n</i>‑octylphosphine Oxide: Thermodynamic Modeling

Tri<i>n</i>-octylphosphine oxide (TOPO) is a widely used extractant because of its high extractive ability. However, there is no systematic research on the thermodynamics of TOPO/<i>n</i>-dodecane in the separation of hydrochloric acid (HCl) from aqueous solution. In this study, the liquid–liquid equilibrium (LLE) system (water + <i>n</i>-dodecane + TOPO + HCl) was investigated. Both the equimolar series and slope methods were used to determine the composition of the complex formed in the equilibrated organic phase. The form of the water molecules in the equilibrated organic phase was first investigated by the thermodynamic method. The thermodynamic model was established with the Pitzer equation for aqueous phase and both Margules and organic Pitzer equations for the organic phase. Two chemical equilibrium constants and their corresponding interaction parameters were regressed from experimental LLE data. The correlated results were in good agreement with the experimental data. Furthermore, this model can also be used to predict the organic phase composition for this system. This confirmed that the thermodynamic model chosen was suitable for the extraction system

Pt/C Electrocatalysts with High Pt Density: A Case Study on Oxygen Reduction Performance from Rotating Disk Electrode to Membrane Electrode Assembly

For the economical deployment of proton exchange membrane fuel cells (PEMFCs), achieving both ultralow platinum (Pt) loading and superior catalytic performance at the membrane electrode assembly (MEA) level is paramount. Despite the significant advancements over the past decade in the development of potent Pt-based catalysts for the oxygen reduction reaction (ORR), the high activities documented using rotating disk electrode (RDE) evaluations often do not manifest comparably in MEA applications. In this study, we delved into the intricate interplay between the catalyst layer (CL) fabrication and its consequent MEA performance. Using a liquid-phase reduction method, we synthesized active Pt/C catalysts at varied loadings: 20 wt % Pt/C, 40 wt % Pt/C, and 70 wt % Pt/C. Intriguingly, even at the 70 wt % threshold, transmission electron microscopy and powder X-ray diffraction characterizations revealed a consistent distribution of Pt nanoparticles across the carbon substrate, coupled with an evident crystalline nature. This dispersion, in tandem with the desirable particle size range of 2–6 nm, underscores the robustness of our methodological approach. RDE analyses suggest that our synthesized catalysts outpace commercially accessible Pt/C variants of similar Pt wt %. However, when the data were transferred to MEA settings, notable deviations from RDE findings emerged, pinpointing the escalating role of mass transfer within the ORR framework. This observation found further resonance in our subsequent COMSOL simulations, underscoring the determinant role of mass transfer in MEA efficacy. This research paves the way for a more discerning approach to CL design, holding significant promise for the enhancement of future PEMFCs