Al–Air Batteries: Fundamental Thermodynamic Limitations from First-Principles Theory

Abstract

The Al-air battery possesses high theoretical specific energy (4140 W h/kg) and is therefore an attractive candidate for vehicle propulsion. However, the experimentally observed open-circuit potential is much lower than what bulk thermodynamics predicts, and this potential loss is typically attributed to corrosion. Similarly, large Tafel slopes associated with the battery are assumed to be due to film formation. We present a detailed thermodynamic study of the Al-air battery using density functional theory. The results suggest that the maximum open-circuit potential of the Al anode is only -1.87 V versus the standard hydrogen electrode at pH 14.6 instead of the traditionally assumed -2.34 V and that large Tafel slopes are inherent in the electrochemistry. These deviations from the bulk thermodynamics are intrinsic to the electrochemical surface processes that define Al anodic dissolution. This has contributions from both asymmetry in multielectron transfers and, more importantly, a large chemical stabilization inherent to the formation of bulk Al(OH)3 from surface intermediates. These are fundamental limitations that cannot be improved even if corrosion and film effects are completely suppressed.

Theoretical Limits to the Anode Potential in Aqueous Mg–Air Batteries

“…computational electrocatalysis, 6 the nonaqueous Li-air battery, 16 the aqueous Zn-air battery, 17 and the aqueous Al-air battery. 18 We outline the following hydroxide-assisted anodic dissolution mechanism similar to one proposed by D. D. Macdonald et al based on experimental data, 19 which is strengthened by theoretical studies on the role of electronegative species in breaking metal-metal bonds 20 and in the anodic dissolution of Al. 18 We find that Cl − adsorption is much weaker than OH − adsorption at pH 10.4, so that hydroxide-assisted dissolution (rather than chloride-assisted dissolution) dominates in a saline electrolyte (a detailed discussion can be found in Figure S2 in the Supporting Information [SI]).…”

Theoretical Limiting Potentials in Mg/O2 Batteries

“…Due to their high concentration, terrace sites likely comprise the majority of sites accessed at the high current densities required for automotive applications. 37,40 Restricting our analysis of the Orich-1 surface only to terrace-site reactions results in a further reduction in overvoltages [0.18 (0.07) V for discharge (charge), Table 2], and a correspondingly higher efficiency of 92%.…”

Recent Progress and Future Trends of Aluminum Batteries

“…20) is 2.74 V, [122][123] the practical voltages are limited to 1.2 to 1.6 V because of the intricate electrode processes occurring at the Al anode. 20) is 2.74 V, [122][123] the practical voltages are limited to 1.2 to 1.6 V because of the intricate electrode processes occurring at the Al anode.…”

“…[119][120]138] To replace the expensive rare catalyst, some cheap composites, such as Fe 3 O 4 , [139] Co 3 O 4 , [140][141] LaMnO 3 , [142] MnCo 2 O 4 , [143][144] MnO x , [145][146][147] FeÀ CÀ N, [148] CoOÀ CÀ N, [149][150] perovskites, [119,142] and so on [151] have been investigated. [123] These deviations are ascribed to the electrochemical surface processes that define Al anodic dissolution. [107,120] Nevertheless, even if the side reactions are complete suppressed, the traditionally assumed Al potential value of À 2.34 V vs. NHE can not be achieved.…”