Engineering the Low Coordinated Pt Single Atom to Achieve the Superior Electrocatalytic Performance toward Oxygen Reduction

Abstract

Configuring metal single‐atom catalysts (SACs) with high electrocatalytic activity and stability is one efficient strategy in achieving the cost‐competitive catalyst for fuel cells’ applications. Herein, the atomic layer deposition (ALD) strategy for synthesis of Pt SACs on the metal–organic framework (MOF)‐derived N‐doped carbon (NC) is proposed. Through adjusting the ALD exposure time of the Pt precursor, the size‐controlled Pt catalysts, from Pt single atoms to subclusters and nanoparticles, are prepared on MOF‐NC support. X‐ray absorption fine structure spectra determine the increased electron vacancy in Pt SACs and indicate the Pt–N coordination in the as‐prepared Pt SACs. Benefiting from the low‐coordination environment and anchoring interaction between Pt atoms and nitrogen‐doping sites from MOF‐NC support, the Pt SACs deliver an enhanced activity and stability with 6.5 times higher mass activity than that of Pt nanoparticle catalysts in boosting the oxygen reduction reaction (ORR). Density functional theory calculations indicate that Pt single atoms prefer to be anchored by the pyridinic N‐doped carbon sites. Importantly, it is revealed that the electronic structure of Pt SAs can be adjusted by adsorption of hydroxyl and oxygen, which greatly lowers free energy change for the rate‐determining step and enhances the activity of Pt SACs toward the ORR.

An Adjacent Atomic Platinum Site Enables Single‐Atom Iron with High Oxygen Reduction Reaction Performance

“…As observed in Figure 2 f, the Fe K ‐edge XANES profile (orange line) shows the edge energy ( E 0 ) value of Fe‐N 4 /Pt‐N 4 located between Fe foil and Fe 2 O 3 , confirming that the average oxidation state of Fe was positively charged below +3, consistent with the Fe 2p XPS result in Figure S19c. The Pt‐ L 3 edge adsorption fine structure in Figure 2 g shows that the Pt in the Fe‐N 4 /Pt‐N 4 is in the same oxidation state around +2, matching well with the previously reported literatures [19, 27b, 28] and Figure S19d. The coordination configurations were determined by the Fourier transformed (FT) EXAFS (Figure 2 h).…”

“…After deconvoluting the Fe 2p signal, Fe 2p spectrum was resolved into doublet peaks of Fe 2+ peaks (709.8 eV), Fe 3+ peaks (710.8 eV) and a weak satellite peak (717.5 eV), indicating the dominated oxidation of Fe‐N 4 between +2 and +3 with the formation of Fe‐N coordination. Meanwhile, the Pt 4f was deconvoluted into two peaks of Pt 4f 7/2 at 72.3 eV and Pt 4f 5/2 at 75.6 eV, which was attributed to the specie of Pt II after formation of Pt−N bonds [28] . No metallic Fe 0 or Pt 0 were observed, further excluding the Fe or Pt nanoparticles in the synthesized samples.…”

Rational Design of Single‐Atom Site Electrocatalysts: From Theoretical Understandings to Practical Applications

“…Sun and co-workers reported a low coordinated Pt single atom supported on the MOF-derived NC materials via ALD technology. [204] The deposition time of Pt on support was explored in this work, and they found that with the increase of time, the sizes of Pt composition became larger, from single atom to cluster and nanoparticles. When the deposition time is 30 s, the well-dispersed atomic Pt SAs-ZIF-NC are obtained, as shown in Figure 16a-d.…”

“…Xiong et al synthesized a Ni-N 4 active sites supported on the carbon spheres with various geometric structures (Ni/HMCS) via template sacrificial agent (SiO 2 ) (Figure 4h-j). [57] The asfabricated Ni/HMCS catalyst shows an enhanced CO 2 RR [51] Copyright 2016, The Authors, published by Springer Nature. f) Most stable geometric structures of Mo x (x = 1-4) supported on the GDY monolayer.…”

“…i,j) TEM image of Pt@PCM with different shell thickness. h-j) Reproduced with permission [57]. Copyright 2020, Wiley-VCH.…”