Enhancement of the performance of Pd nanoclusters confined within ultrathin silica layers for formic acid oxidation

Efficient hydrogen production from formic acid dehydrogenation over ultrasmall PdIr nanoparticles on amine-functionalized yolk-shell mesoporous silica

Developing heterogeneous catalysts with exceptional catalytic activity over formic acid (HCOOH, FA) dehydrogenation is imperative to employ FA as an effective hydrogen (H2) carrier. In this work, ultrasmall (1.4 nm) and well-dispersed PdIr nanoparticles (NPs) immobilized on amine-functionalized yolk-shell mesoporous silica nanospheres (YSMSNs) with radially oriented mesoporous channels have been synthesized by a co-reduction strategy. The optimized catalyst Pd4Ir1/YSMSNs-NH2 (Pd/Ir molar ratio = 4:1) exhibited a remarkable turnover frequency (TOF) of 5818 h-1 and remarkable stability at 50 °C with the addition of sodium formate (SF), resulting in complete FA conversion and H2 selectivity, exceeding most of the solid heterogeneous catalysts in previous reports under similar circumstances. Kinetic isotope effect (KIE) exploration indicates the cleavage of the CH bond is regarded as the rate-determining step (RDS) during the FA dehydrogenation process. Such excellent catalytic properties arise from the ultrafine and well-dispersed PdIr NPs supported on the nanosphere support YSMSNs-NH2, the electronic synergistic effect of PdIr alloy NPs, and the strong metal-support interaction (MSI) effect between the introduced PdIr NPs and YSMSNs-NH2 support. This work offers a new paradigm for exploiting the highly effective silica-supported Pd-based heterogeneous catalysts over the dehydrogenation of FA.

Catalyst Composites of Palladium and N-Doped Carbon Quantum Dots-Decorated Silica and Reduced Graphene Oxide for Enhancement of Direct Formic Acid Fuel Cells

Pd-based catalysts consisting of Pd nanoparticles on nitrogen-doped carbon quantum dots (N-CQDs) modified silica (SiO₂) and reduced graphene oxide have been synthesized through reduction for use as catalysts for improved formic acid oxidation. The structure, morphology, chemical composition, functional groups, and porosity of the synthesized catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared (FT-IR) spectroscopy, Raman spectroscopy, and Brunauer-Emmett-Teller (BET) spectroscopy, respectively. Their electrocatalytic activities were also evaluated by electrochemical measurements. The differences in the average particle sizes found for Pd/N-CQDs-SiO₂-rGO, Pd/N-CQDs-rGO, and Pd/rGO were 4.81, 5.56, and 6.31 nm, respectively. It was also found that the Pd/xN-CQDs-SiO₂-yrGO composite catalysts (where x and y is 1 to 4) can significantly improve the activity and stability toward formic acid electrooxidation compared with Pd/rGO and commercial Pt/C. The mass activities of Pd/N-CQDs-SiO₂-rGO, Pd/N-CQDs-rGO, and Pd/rGO were 951.4, 607.8, and 157.6 mA g^-1, respectively, which was ca. 6-7 times compared with Pd/rGO and approximately 3-4 times compared with commercial Pt/C. With low potential for CO oxidation and high current intensity, the composites of rGO, SiO₂, and N-CQDs into Pd-based catalysts improved the catalytic activity of the prepared catalyst for the oxidation of formic acid in acidic media. The value of the Tafel slope designated that the chief path of the prepared catalysts is the dehydrogenation process. These prepared catalysts exhibit promise toward the development of high-performance Pd-based electrocatalysts for formic acid oxidation.

Hollow Pd/Te nanorods for the effective electrooxidation of methanol

Methanol electrooxidation is significant in realizing effective C1 liquid fuel applications. Herein, hollow Pd/Te nanorods were fabricated and evaluated for methanol oxidation, and they were found to exhibit high catalytic efficiency for methanol oxidation in alkaline electrolyte compared to Pd or Pd/C catalysts. The hybrid structure of hexagonal crystal Te and face-centered cubic Pd was formed by microwave assisted Pd nanoparticle deposition over the surface of Te nanorods. Strong electronic effects and facile oxophilic properties were indicated in the Pd/Te system by spectroscopic analysis, which mainly accounts for the high catalytic performance for methanol oxidation. Specifically, they showed a peak current density of 90.1 mA cm^-2 for methanol oxidation, around 3.5 times higher than that of commercial Pd/C (26.3 mA cm^-2). High catalytic stability was also observed for Pd/Te, with a current retention of 64.3% after 3600 s of chronoamperometric testing, much higher than for Pd catalysts (20.1%). High anti-CO poisoning ability of the Pd/Te catalyst was demonstrated in the CO-stripping voltammetry results, and faster catalytic kinetics were also observed for this catalyst system. The electron-rich state of Pd and high active site exposure are responsible for the high performance of the Pd/Te catalyst in methanol oxidation.

Recent advances in formic acid electro-oxidation: from the fundamental mechanism to electrocatalysts

Direct formic acid fuel cells have attracted significant attention because of their low fuel crossover, high safety, and high theoretical power density among all the proton-exchange membrane fuel cells. Much effort has been devoted to the study of formic acid oxidation, including the reaction processes and electrocatalysts. However, as a model reaction, the anodic electro-oxidation process of formic acid is still not very clear, especially regarding the confirmation of the intermediates, which is not helpful for the design and synthesis of high-performance electrocatalysts for formic acid oxidation or conducive to understanding the reaction mechanisms of other small fuel molecules. Herein, we briefly review the recent advances in investigating the mechanism of formic acid electro-oxidation and the basic design concepts of formic acid oxidation electrocatalysts. Rather than an exhaustive overview of all aspects of this topic, this mini-review mainly outlines the progress of this field in recent years.