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Single Pt atom catalysts show enhanced catalytic activity for water-splitting; potential to drive down electrolysis cost

A research team from University of Western Ontario, McMaster University and Beijing Computational Science Research Center has developed an effective synthesis method to produce isolated single platinum (Pt) atoms and clusters for use as catalysts for the hydrogen evolution reaction (HER) in water splitting to produce hydrogen.

In an open-access paper published in Nature Communications, the researchers reported that the single Pt atom catalysts exhibit significantly enhanced catalytic activity (up to 37 times) and high stability in comparison to the state-of-the-art commercial platinum/carbon (Pt/C) catalysts.

Platinum-based catalysts are generally considered to be the most effective electrocatalysts for the HER. Unfortunately, Pt is expensive and scarce, limiting the commercial potential for such catalysts. Significant effort has been devoted to the search of non-precious-metal based HER catalysts including sulfide-based materials, and C3N4. Although these candidate materials show promising activities for the HER, the activities of these catalysts in their present form are insufficient for industrial applications.

To overcome the challenges associated with the Pt HER catalysts and to drive the cost of H2 production from water electrolysis down, it is very important to markedly decrease the Pt loading and increase the Pt utilization efficiency.

—Cheng et al.

In this work, the team fabricated single platinum atoms and clusters supported on nitrogen-doped graphene nanosheets (NGNs) using atomic layer deposition (ALD). The size and density of the Pt catalysts on the NGNs are precisely controlled by simply adjusting the number of ALD cycles. The researchers also prepared single Pt atoms on graphene to compare with the samples on N-doped graphene.

Ncomms13638-f1
Schematic illustration of the Pt ALD mechanism on NGNs. The ALD process includes the following: the Pt precursor (MeCpPtMe3) first reacts with the N-dopant sites in the NGNs (i). During the following O2 exposure, the Pt precursor on the NGNs is completely oxidized to CO2 and H2O, creating a Pt containing monolayer (ii). These two processes (i and ii) form a complete ALD cycle. During process (ii), a new layer of adsorbed oxygen forms on the platinum surface, which provides functional groups for the next ALD cycle process (iii). Cheng et al. Click to enlarge.

The researchers found that the stability of the single Pt atoms on pure graphene was low, resulting in the loss of 24% of the initial HER activity after stability tests. On the other hand, the single Pt atoms on the N-doped graphene resulted in a decreased activity of only 4%.

We found that the interaction between the metal atoms and the support plays a vital role in the stabilization.

—Dr. Niancai Cheng, lead author, University of Western Ontario

First-principles calculations showed that the interaction energy between the single Pt atoms and N-dopants is about 5.3 eV, which is approximately 3.4 eV larger than the bond strength between the Pt atoms on the graphene substrate, suggesting that the Pt prefers to bind to the N-sites.

The researchers also studied the mechanisms of the single-atom catalysis. X-ray absorption fine structure (XAFS) and density functional theory (DFT) analyses indicated that the partially unoccupied density of states of the Pt atoms’ 5d orbitals on the N-doped graphene are responsible for the excellent performance.

Understanding mechanisms of the single-atom catalysis and stabilization of single atoms will provide insights into the design of high performance catalytic systems. This may provide us a new insight for industrial catalyst design.

—Dr. Xueliang Sun, co-corresponding author, University of Western Ontario

Resources

  • Niancai Cheng, Samantha Stambula, Da Wang, Mohammad Norouzi Banis, Jian Liu, Adam Riese, Biwei Xiao, Ruying Li, Tsun-Kong Sham, Li-Min Liu, Gianluigi A. Botton & Xueliang Sun (2016) “Platinum single-atom and cluster catalysis of the hydrogen evolution reaction” Nature Communications 7, Article number: 13638 doi: 10.1038/ncomms13638

Comments

HarveyD

If this process can be repeated and mass produced, it could become a major breakthrough for the production of clean H2 using clean regular or excess REs.

With a potential 37X increase in performance, the production cost of clean H2 could come down drastically?

Future all weather extended range (400+ miles) FCEVs operation cost could compare with equivalent BEVs?

Dr. Strange Love

Nitrogen is more electronegative than Carbon. That explains the 3.4eV extra bonding potential. 5d did contribute. It is a transition metal. What else do we know?

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