An Overview on Pt3 X Electrocatalysts for Oxygen Reduction Reaction

Effects of Zr dopants on properties of PtNi nanoparticles for ORR catalysis: A DFT modeling

Pt-based alloys, such as Pt3Ni, are among the best electrocatalysts for oxygen reduction reaction (ORR) in polymer electrolyte membrane fuel cells. Doping of PtNi alloys with Zr was shown to enhance the durability of the operating ORR catalysts. Rationalizing these observations is hindered by the absence of atomic-level data for these tri-metallic materials, even when not exposed to the fuel cell operation conditions. This study aims at understanding structure-property relations in Zr-doped PtNi nanoparticles as a key to their ORR function. In particular, we calculated, using a method based on density functional theory, the most stable chemical orderings of pristine and Zr-doped Pt3Ni particles containing over 400 atoms. We thus clarify (i) preferential location and charge states of Zr atoms in the Pt3Ni NPs; (ii) effect of doping Zr atoms on the stability of the Pt skin of the Pt3Ni NPs; (iii) charge redistribution induced by Zr dopants; (iv) layer-by-layer atomic ordering in the Pt3Ni/Zr NPs with the increasing Zr content; and (v) effect of Zr atoms on the adsorption energies of O and OH species as indicators of the ORR activity.

Advances on Axial Coordination Design of Single-Atom Catalysts for Energy Electrocatalysis: A Review

Single-atom catalysts (SACs) have garnered increasingly growing attention in renewable energy scenarios, especially in electrocatalysis due to their unique high efficiency of atom utilization and flexible electronic structure adjustability. The intensive efforts towards the rational design and synthesis of SACs with versatile local configurations have significantly accelerated the development of efficient and sustainable electrocatalysts for a wide range of electrochemical applications. As an emergent coordination avenue, intentionally breaking the planar symmetry of SACs by adding ligands in the axial direction of metal single atoms offers a novel approach for the tuning of both geometric and electronic structures, thereby enhancing electrocatalytic performance at active sites. In this review, we briefly outline the burgeoning research topic of axially coordinated SACs and provide a comprehensive summary of the recent advances in their synthetic strategies and electrocatalytic applications. Besides, the challenges and outlooks in this research field have also been emphasized. The present review provides an in-depth and comprehensive understanding of the axial coordination design of SACs, which could bring new perspectives and solutions for fine regulation of the electronic structures of SACs catering to high-performing energy electrocatalysis.

Morphology-Tuned Pt3 Ge Accelerates Water Dissociation to Industrial-Standard Hydrogen Production over a wide pH Range

The discovery of novel materials for industrial-standard hydrogen production is the present need considering the global energy infrastructure. A novel electrocatalyst, Pt₃ Ge, which is engineered with a desired crystallographic facet (202), accelerates hydrogen production by water electrolysis, and records industrially desired operational stability compared to the commercial catalyst platinum is introduced. Pt₃ Ge-(202) exhibits low overpotential of 21.7 mV (24.6 mV for Pt/C) and 92 mV for 10 and 200 mA cm^-2 current density, respectively in 0.5 m H₂ SO₄ . It also exhibits remarkable stability of 15 000 accelerated degradation tests cycles (5000 for Pt/C) and exceptional durability of 500 h (@10 mA cm^-2 ) in acidic media. Pt₃ Ge-(202) also displays low overpotential of 96 mV for 10 mA cm^-2 current density in the alkaline medium, rationalizing its hydrogen production ability over a wide pH range required commercial operations. Long-term durability (>75 h in alkaline media) with the industrial level current density (>500 mA cm^-2 ) has been demonstrated by utilizing the electrochemical flow reactor. The driving force behind this stupendous performance of Pt₃ Ge-(202) has been envisaged by mapping the reaction mechanism, active sites, and charge-transfer kinetics via controlled electrochemical experiments, ex situ X-ray photoelectron spectroscopy, in situ infrared spectroscopy, and in situ X-ray absorption spectroscopy further corroborated by first principles calculations.

In Situ Mechanistic Insights for the Oxygen Reduction Reaction in Chemically Modulated Ordered Intermetallic Catalyst Promoting Complete Electron Transfer

The well-known limitation of alkaline fuel cells is the slack kinetics of the cathodic half-cell reaction, the oxygen reduction reaction (ORR). Platinum, being the most active ORR catalyst, is still facing challenges due to its corrosive nature and sluggish kinetics. Many novel approaches for substituting Pt have been reported, which suffer from stability issues even after mighty modifications. Designing an extremely stable, but unexplored ordered intermetallic structure, Pd₂Ge, and tuning the electronic environment of the active sites by site-selective Pt substitution to overcome the hurdle of alkaline ORR is the main motive of this paper. The substitution of platinum atoms at a specific Pd position leads to Pt_0.2Pd_1.8Ge demonstrating a half-wave potential (E_1/2) of 0.95 V vs RHE, which outperforms the state-of-the-art catalyst 20% Pt/C. The mass activity (MA) of Pt_0.2Pd_1.8Ge is 320 mA/mg_Pt, which is almost 3.2 times better than that of Pt/C. E_1/2 and MA remained unaltered even after 50,000 accelerated degradation test (ADT) cycles, which makes it a promising stable catalyst with its activity better than that of the state-of-the-art Pt/C. The undesired 2e^- transfer ORR forming hydrogen peroxide (H₂O₂) is diminished in Pt_0.2Pd_1.8Ge as visible from the rotating ring-disk electrode (RRDE) experiment, spectroscopically visualized by in situ Fourier transform infrared (FTIR) spectroscopy and supported by computational studies. The effect of Pt substitution on Pd has been properly manifested by X-ray absorption spectroscopy (XAS) and X-ray photoelectron spectroscopy (XPS). The swinging of the oxidation state of atomic sites of Pt_0.2Pd_1.8Ge during the reaction is probed by in situ XAS, which efficiently enhances 4e^- transfer, producing an extremely low percentage of H₂O₂.

Facile Synthesis of Surfactant-Induced Platinum Nanospheres with a Porous Network Structure for Highly Effective Oxygen Reduction Catalysis

Developing a facile and eco-friendly method for the large-scale synthesis of the highly active and stable catalysts toward oxygen reduction reaction (ORR) is very important for the practical application of proton exchange membrane fuel cells (PEMFCs). In this paper, a mild aqueous-solution route has been successfully developed for the gram-scale synthesis of three-dimensional porous Pt nanospheres (Pt-NSs) that are composed of network-structured nanodendrites and/or oval multipods. In comparison with the commercial Pt/C catalyst, X-ray photoelectron spectroscopy (XPS) demonstrates the dominant metallic-state of Pt and electrochemical impedance spectroscopy (EIS) indicates the substantial improvement of conductivity for the Pt-NSs/C catalyst. The surfactant-induced porous network nanostructure improves both the catalytic ORR activity and durability. The optimal Pt-NSs/C catalyst exhibits a half-wave potential of 0.898 V (vs. RHE), leading to the mass activity of 0.18 A mgPt-1 and specific activity of 0.68 mA cm-2 which are respectively 1.9 and 5.7 times greater than those of Pt/C. Moreover, the highly-active Pt-NSs/C catalyst shows a superior stability with the tenable morphology and the retained 78% of initial mass activity rather than the severe Pt aggregation and the only 58% retention of the commercial Pt/C catalyst after 10000 cycles.