9 9 I H I G H L I G H T S 2 0 2 1
PRINCIPAL PUBLICATION AND AUTHORS
Multiphase, multiscale chemomechanics at extreme low temperatures: battery electrodes for operation in a wide temperature range, J. Li (a), S. Li (a), Y. Zhang (b), Y. Yang (c,d), S. Russi (a), G. Qian (a), L. Mu (b), S.-J. Lee (a), Z. Yang (b), J.-S. Lee (a), P. Pianetta (a), J. Qiu (e), D. Ratner (a), P. Cloetens (c), K. Zhao (f), F. Lin (b), Y. Liu (a), Adv. Energy Mater. 37, 2102122 (2021); https:/doi.org/10.1002/aenm.202102122 (a) SLAC National Accelerator Laboratory, Menlo Park (USA) (b) Virginia Tech, Blacksburg (USA) (c) ESRF (d) Brookhaven National Laboratory, Upton (USA) (e) Dalian University of Technology, Dalian (China) (f) Purdue University, West Lafayette (USA)
 J. Zhang et al., Nat. Commun. 11, 6342 (2020).  Z. Jiang et al., Nat. Commun. 11, 2310 (2020).
Methane-cycling microfossils found in 3.4-billion-year-old subseafloor rock
Fossilised remains of microbes discovered in hydrothermal veins in South Africa suggest that some of the earliest known organisms were methane- cycling and lived underground. These microfossils lived 3.42 billion years ago, are the oldest evidence for this type of life and expand the frontiers of potentially habitable environments on the early Earth.
Microfossils were found within rocks collected from the Onverwacht Group in South Africa s Barberton Greenstone Belt, which contains some of the oldest
and best-preserved sedimentary rocks found on our planet. Back at the lab, the filamentous structures were analysed intensively with microscopy and spectroscopy to reveal their morphologies, fine-structure and chemical composition over a range of scales (Figure 79). The traces of carbon, hydrogen, nitrogen, sulfur and oxygen detected in the filamentous structures strongly support the theory that they were remnants from ancient microbes with a carbon-rich outer sheath and a chemically and structurally distinct core, consistent with a cell wall or membrane around intracellular or cytoplasmic matter.
Micro- and nano-X-ray imaging were performed at beamlines ID21 and ID16B respectively, to probe the elemental composition and speciation in the tender (2 to 9 keV) and hard (6 to 30 keV) X-ray energy regions. Synchrotron nano-X-ray fluorescence (XRF) imaging carried out on focused-ion-beam (FIB) sectioned filaments reveals trace amounts of sulfur (S), one of the major bioessential elements, whereas the unique nickel (Ni) K-edge spectra, acquired by nano-XANES, reveal the presence of specific Ni-organic compounds (Figure 80). Ni is an important metal cofactor in the biological process of microbial methanogenesis. The microfossil Ni content (2.78 × 107 ± 1.95 × 106 at μm−3 equivalent to 0.46 ± 0.03 mM) is also consistent with Ni content found in modern microbes known as Archaea prokaryotes , which live in the absence of oxygen and use methane for their metabolism. Although, it is known that Archaea
Fig. 79: Optical microscopy image of a rock slice showing a cluster of 3.42-billion-year-old kerogenous filamentous microfossils (average diameter: ~0.77 μm). Image: @Cavalazzi.
Fig. 80: Nickel distribution in kerogenous filamentous microfossils. a) High-spatial- resolution map of the distribution of Ni of a filament analysed in a FIB cross-sectioned filament. The map was acquired at 17 keV (dwell time: 0.5 s; pixel size: 55 nm). b) Nano-XANES spectra of the filament (red line) from (a) and of a Rhône-Poulenc NiO standard (blue line). The boxed area in (b) is magnified in the right side and shows details of the ∆E edge shift used for valence estimation (arrows). Error bars are within the linewidth for NiO and are plotted in grey for the filament. AU: arbitrary units.