An Inexpensive and Earth-Abundant Aluminium Based Single Atom Catalyst for Efficacious Oxygen Reduction Reaction

ABSTRACT Oxygen reduction reaction (ORR) is crucial for the commercial success of environmentally benign energy conversion devices such as fuel cells and metal−air batteries [1-2]. Replacement of Pt-based and transition metal-based electrocatalysts with efficient non-precious ORR catalysts is quite challenging so for [3-5]. Single-atom catalysts (SACs) based on first-row transition metals like Fe, Co, Cr have already received significant attention for ORR [6]. In this hunt, we have developed the rarely explored P-block earth abundant aluminium-based efficient and cost-effective ORR single atom catalyst. Nitrogen-doped Aluminium-based single atom catalyst has been synthesised by pyrolyzing aluminium phthalocyanine (AlPc) with dicyandiamide (DCDA) which is the source of carbon and nitrogen at different temperature and characterized by X-ray diffraction, X-ray photoelectron spectroscopy, transmission electron microscopy. For comparison, AlPc has been pyrolyzed at 1000 °C without the addition of DCDA. The catalysts are named Al-N-C/T (T = 700 °C - 1000 °C) depending on the pyrolysis temperature. AlPc/1000 showed poor ORR activity with low diffusion-limited current of 0.76 mA/cm2 (current measured at the potential of 0.3 V vs RHE). The insufficient catalytic activity of AlPc-1000 is due to the strong bonding of aluminium active centers with oxygenated group intermediate. But after the introduction of DCDA, the catalytic activity of Al-N-C/T (T = 700 °C - 1000 °C) has been improved significantly because N-bonded Al atoms have optimal bonding strength with intermediate oxygen species [7]. The coordination environment of Al-N-C plays an essential role in exhibiting excellent catalytic activity towards ORR. The Al-N-C/1000 catalyst exhibits the highest diffusion-limited current (4.49 mA/cm2) as compared to all other Al-N-C/T (T = 700, 800, and 900 °C) based catalysts, along with more positive Eonset (844 mV vs. RHE) and half-wave potential E1/2 (749 mV vs RHE) (Figure 1). Electrochemical calculation further ropes the Al-Nx sites as the origin of ORR via an efficient 4-electron transfer pathway in basic medium. Importantly, negligible reduction in current density after 9000 cycles in alkaline medium is far superior to the durability limit set by the US department of energy and overpasses the state-of-the-art Pt/C catalyst (Figure 1). This methodology can be applied to design a variety of other alkaline earth, P block effective electrocatalysts. The Al-N-C/1000 catalyst exhibits the highest diffusion-limited current as compared to all other Al-N-C/T (T = 700, 800, and 900 °C) based catalysts, along with more positive Eonset and half wave potential. Electrochemical calculation further ropes the Al-Nx sites as the origin of ORR via an efficient 4-electron transfer pathway in basic medium. Importantly, negligible reduction in current density after 9000 cycles in alkaline medium is far superior to the durability limit set by the US department of energy and overpasses the state-of-the-art Pt/C catalyst. This methodology can be applied to design a variety of other alkaline earth, P block effective electrocatalysts. Keywords:ORR; Al-N-C electrocatalyst; SAC; P-block; Excellent stability References: [1] G. Wu et al., Energy Environ. Sci. 12, 250–260 (2019). [2] J. Wang et al., Appl. Mater. Today. 13, 174–181 (2018). [3] Z.D. Wei et al., Chem. Soc. Rev. 44, 2168−2201 (2015). [4] S. H. A. Yu et al., Adv. Mater. 23, 1467−1471 (2011). [5] Y. Huang et al., Science. 348, 1230−1234 (2015). [6] Y. Lin et al., Adv. Energy Mater. 8, 1–8 (2018) [7] Q. Chen et al., Nat. Commun. 11,938 (2020) Figure 1