Inhibition of Ostwald ripening through surface switching species during potentiodynamic dissolution of platinum nanoparticles as an efficient strategy for platinum group metal (PGM) recovery

An Effective Route to Enhance Pt/C Electrocatalyst Durability through Addition of Ceramic Nanoparticles to Facilitate Pt Redeposition

Platinum particle growth during long-term operations is one of the well-known bottlenecks offsetting the performance and stability of Pt-based electrocatalysts in polymer electrolyte membrane (PEM) fuel cells and PEM water electrolyzers. In this research, the addition of certain ceramic nanoparticulate additives to the catalyst ink was evaluated as a means of improving the electrochemical stability of a carbon-supported platinum (Pt/C) electrocatalyst in gas diffusion electrodes (GDEs) during an accelerated stress test (AST). GDEs prepared using three nanoparticulate ceramic additives (TiN, ATO, and TiO2) with three loadings (replacing 5, 10, and 15 wt % of the catalyst) were studied for their electrochemical performance, i.e., the initial electrochemical surface area (ECSA) and stability during AST in a liquid cell. TiN appeared to be an optimal additive among the three to (i) improve the stability by ∼40% during 1600 cycles, (ii) prohibit Pt nanoparticle agglomeration due to coalescence and Ostwald ripening, and (iii) reduce Pt dissolution during the AST, without compromising a high initial ECSA. The fundamental mechanism lies in the fact that the ceramic nanoparticles can act as additional nucleation sites for redeposition of the dissolved Pt during AST; X-ray photoelectron spectroscopy (XPS) indicates strong interactions between platinum and ceramic nanoparticles. Eventually, the superior sample was used as the cathode catalyst in an electrolyzer to compare the electrochemical performance with that of a commercial Pt/C sample. As confirmed by single-cell tests in this research, the method studied and the associated concept here to enhance the durability of Pt-based electrocatalysts are facile and scalable and hence may be readily adopted by relevant stakeholders.

Scalable Solid-State Synthesis of Carbon-Supported Ir Electrocatalysts for Acidic Oxygen Evolution Reaction: Exploring the Structure-Activity Relationship

Enhancing iridium (Ir)-based electrocatalysts to achieve high activity and robust durability for the oxygen evolution reaction (OER) in acidic environments has been an ongoing mission in the commercialization of proton exchange membrane (PEM) electrolyzers. In this study, we present the synthesis of carbon-supported Ir nanoparticles (NPs) using a modified impregnation method followed by solid-state reduction, with Ir loadings of 20 and 40 wt % on carbon. Among the catalysts, the sample with an Ir loading of 20 wt % synthesized at 1000 °C with a heating rate of 300 °C/h demonstrated the highest mass-normalized OER performance of 1209 A gIr-1 and an OER current retention of 80% after 1000 cycles of cyclic voltammetry (CV). High-resolution STEM images confirmed the uniform dispersion of NPs, with diameters of 1.6 ± 0.4 nm across the support. XPS analysis revealed that the C-O and C═O peaks shifted slightly toward higher binding energies for the best-performing catalyst. In comparison, the metallic Ir state shifted toward lower binding energies compared to other samples. This suggests electron transfer from the carbon support to the Ir NPs, indicating a potential interaction between the catalyst and the support. This work underscores the strong potential of the solid-state method for the scalable synthesis of supported Ir catalysts.

L3-edge X-ray spectroscopy of rhodium and palladium compounds

L3-edge high-energy-resolution fluorescence-detection X-ray absorption near-edge structure (XANES) spectra for palladium and rhodium compounds are presented, with focus on their electronic structures. The data are compared with transmission XANES spectra recorded at the K-edge. A correlation between the absorption edge energy and the metal ion oxidation state is not observed. Despite the different filling of the 4d orbitals and different local coordination, the Rh and Pd compounds show remarkably similar spectral shapes. Calculation of the density of states and of the L3-XANES data reproduce the experimental results.

Tailoring iridium-palladium nanoparticles with Ir-rich skin: a highly durable anode electrocatalyst for acidic water electrolysis via a facile microwave-assisted chemical reduction method

Electrochemical water splitting under acidic conditions is a clean way towards producing hydrogen fuels. The slow kinetics of the oxygen evolution reaction (OER) at the anode is currently a bottleneck for commercial acceptance of this technology. Therefore, arriving at more efficient and sustainable OER electrocatalysts is highly desirable. We here demonstrate the synthesis of iridium-palladium (IrPd) alloy nanoparticles (2-5 nm) with variable average composition (Ir : Pd = 1 : 0, 1 : 1, 1 : 3, 1 : 6, 1 : 9 and 0 : 1) using a facile one-pot microwave-assisted chemical reduction method. The IrPd nanoparticles show structure- and composition-dependent OER performance in acidic media. Utilizing different reduction strengths and precursor ratios, successful alloy catalysts were prepared with Ir-rich skin and sublayers of different Pd compositions. Their structures were revealed using high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy, and hydrogen underpotential deposition (Hupd) studies. It turned out that (1) the alloy OER catalyst also has a high electrochemically active surface area for hydrogen adsorption/desorption, (2) the OER performance is strongly dependent on the surface Ir contribution and (3) the intact Ir skin is essential for electrocatalyst stability.

Multiple Bubble Removal Strategies to Promote Oxygen Evolution Reaction: Mechanistic Understandings from Orientation, Rotation, and Sonication Perspectives

Bubble coverage of catalytically active sites is one of the well-known bottlenecks to the kinetics of the oxygen evolution reaction (OER). Herein, various bubble removal approaches (electrode orientation, rotating, and sonication) were considered for the OER performance evaluation of a state-of-the-art Ir-based electrocatalyst. Key parameters, such as catalyst mass loss, activity, overpotential, and charge- and mass-transfer mechanisms, were analyzed. First, it was suggested that a suitable orientation of the working electrode facilitates coalescence and sliding bubble effects on the catalyst surface, leading to better electrochemical performance than those of the traditional rotating disk electrode (RDE) configuration. Then, the convection and secondary Bjerknes force were explained as the responsible phenomena in improving the OER activity in the RDE and sonication methods. Finally, simultaneous implementation of the methods enhanced the catalyst mass activity up to 164% and provided fast charge-transfer kinetics and low double-layer capacitance, which eventually led to a 22% reduction in overpotential, while the catalyst loss slightly increased from 1.93 to 3.88%.

Influence of Electrochemical Pretreatment Conditions of PtCu/C Alloy Electrocatalyst on Its Activity

A carbon supported PtCu_x/C catalyst, which demonstrates high activity in the oxygen electroreduction and methanol electrooxidation reactions in acidic media, has been obtained using a method of chemical reduction of Pt (IV) and Cu (2+) in the liquid phase. It has been found that the potential range of the preliminary voltammetric activation of the PtCu_x/C catalyst has a significant effect on the de-alloyed material activity in the oxygen electroreduction reaction (ORR). High-resolution transmission electron microscopy (HRTEM) demonstrates that there are differences in the structures of the as-prepared material and the materials activated in different potential ranges. In this case, there is practically no difference in the composition of the PtCu_x-y/C materials obtained after activation in different conditions. The main reason for the established effect, apparently, is the reorganized features of the bimetallic nanoparticles’ surface structure, which depend on the value of the limiting anodic potential in the activation process. The effect of the activation conditions on the catalyst’s activity in the methanol electrooxidation reaction is less pronounced.