"Mineral Membrane"—a Potential OER Interface on Earth's Surface

"Mineral membrane" specially refers to semiconducting Fe and Mn (oxyhydr)oxide mineral coatings that are found to overlay vast expanses of natural rock/soil surfaces, where birnessite is the dominant Mn (oxyhydr)oxides. (Lu et al., 2019a). Remarkably, birnessite is also a typical "biomimetic mineral" for water oxidation, owing to the same Kok's classical S-state cycle and similar cubane structure of oxidant oxygen complex (OEC) in PSII system (Cox et al., 2013).

Besides rare earth elements especially Ce, have been previously found to be slightly enriched in "mineral membrane", in which the Ce:Mn mass ratio could reach 1:20 (Lu et al., 2019b). Hence, Ce was supposed to concentrated in birnessite. Notably, Ce(IV) was the most widely used sacrificial oxidant in OER(oxygen evolution reaction). We thus assumed that the Ce-rich birnessite in "mineral membrane" plays important roles in the abiotic evolution of oxygen.

Therefore, the effect of doping Ceon oxygen evolution was evaluated and compared with Na-birnessite by electrocatalytic studies. The overpotential (η) of Ce-birnessite electrode at a current density of 10 mA cm⁻² for the OER was 610 mV, significantly lower than η = 820 mV of Na-birnessite. Furthermore, the Tafel slope of Ce-birnessite presented a significant decline as compared with Na-birnessite. All these electrochemical results indicated OER activity could be enhanced by incorporating Ce into birnessite. This study contributes to discover the "mineral photosynthesis" of birnessite also plays an important role in the evolution of oxygen for great oxygenation event.

References

Cox, N., Pantazis, D. A., Neese, F. & Lubitz, W. Biological water oxidation. Accounts of chemical research, 2013, 46(7): 1588-1596.

Lu, A., Li, Y., Ding, H., Xu, X., Li, Y., Ren, G., Liang, J., Liu, Y., Hong, H., Chen, N., Chu, S., Liu, F., Li, Y., Wang, H., Ding, C., Wang, C., Lai, Y., Liu, J., Dick, J., Liu, K. & Hochella, M. F. Photoelectric conversion on Earth's surface via widespread Fe- and Mn-mineral coatings. Proceedings of the National Academy of Sciences, 2019a, 116(20): 9741-9746.

Lu, A., Li, Y., Ding, H., Wang, C. Surface "Mineral Membrane": Earth's "New Sphere" Acta Petrologica Sinica, 2019b, 35(01): 119-128.