| dc.description.abstract | The extensive use of fossil fuels has led to a severe energy crisis and environmental challenges, prompting the need to explore sustainable and clean energy sources. Hydrogen is highly valued for its high energy density, feasibility of transport and storage, and energy conversion efficiency in fuel cells. However, the slow reaction kinetics of the cathodic hydrogen evolution reaction (HER) and the anodic oxygen evolution reaction (OER) in water electrolysis result in high overpotentials, posing significant barriers to large-scale hydrogen production. Therefore, designing superior electrocatalysts to achieve optimal overpotentials and efficient water electrolysis is a primary research goal. Pd, with an electronic structure similar to Pt, is a promising alternative to Pt. However, the strong interaction between Pd and hydrogen atoms usually makes hydrogen desorption difficult, leading to poor HER performance.
This study improves the HER process by introducing hydrogen and alloying with a second metal, effectively weakening the strong affinity between Pd and H through strain and ligand effects. We synthesized Pd-based catalysts using a simple oleylamine method to form hydrides, and by adding Ir, we appropriately tuned the catalyst′s hydrogen adsorption energy, enhancing HER performance in acidic environments and improving stability due to Ir′s excellent corrosion resistance. In an acidic environment (0.5 M H2SO4), PdIr0.1H0.2/C and PdIr0.15/C showed excellent HER electrochemical performance with overpotentials of 25 and 28 mV at a current density of 10 mA cm-2, Tafel slopes of 14 and 18 mV dec-1, and mass activities of 1025 and 1064 mA/mg Pd+Ir, respectively. After 5000 cycles of accelerated durability testing, PdIr0.15/C retained 76% of its mass activity, while PdIr0.1H0.2/C retained only 33%. Despite PdIr0.1H0.2/C showing lower initial overpotential and Tafel slope, highlighting the crucial role of H and Ir in enhancing HER performance, PdIr hydrides proved unstable compared to PdIr. Additionally, in-situ X-ray absorption spectroscopy (XAS) and inductively coupled plasma optical emission spectrometry (ICP-OES) analyses provided insights into the stability of PdIr hydride catalysts (PdIr0.1H0.2/C). In-situ XAS results indicated that after stability testing, the coordination numbers of Pd-Pd and Pd-Ir increased compared to the initial state, and the Pd-Pd bond length reverted to that of Pd foil, indicating the departure of initially present hydrogen atoms from the Pd lattice. ICP results revealed that adding hydrogen to PdIr caused Ir dissolution. These findings suggest that hydrogen addition destabilizes the PdIr catalyst structure and leads to Ir dissolution, deteriorating the catalyst stability.
On the other hand, hydrogen addition not only reduces the catalyst′s hydrogen adsorption energy but also enhances stability in alkaline simulated seawater electrolyte (1 M KOH + 3.5 wt% NaCl). PdH0.4/C exhibited an overpotential of 25 mV at 10 mA cm-2, Tafel slope of 40 mV dec-1, and mass activity of 207 mA/mg Pd, retaining 96% of its mass activity after 5000 cycles, demonstrating excellent performance and stability. This study combines the introduction of Ir and H to improve the HER performance of Pd-based catalysts and provides insights into the mechanisms behind their superior performance, offering new perspectives for the rational design of more efficient electrocatalysts. | en_US |