Hematite as an Electrocatalytic Marker for the Study of Archaeological Ceramic Clay bodies: A VIMP and SECM Study**

Abstract

The electrocatalytic effect exerted by hematite, a ubiquitous component of clay bodies, on the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) can be used to acquire information on archaeological ceramics. The solid-state voltammetric response of different hematite and ochre specimens, accompanied by SECM analysis in contact with 0.10 M HCl aqueous solution, is described. In air-saturated solutions, catalytic effects on the ORR and OER are accompanied by Fe(III)/Fe(II) and Fe(IV)/Fe(III) redox reactions. Such processes are conditioned by a variety of factors, the hydroxylation degree of the mineral surfaces being particularly influential, and exhibit significant variations upon heating the specimens between 300 and 900 °C. Voltammetric measurements carried out on a set of archaeological samples of Apulian red-figured pottery dated back within 5 th and 4 th centuries BCE permit to obtain sitecharacteristic voltammetric profiles.

Electrochemical methods to discriminate technology and provenance of Apulian red‐figured pottery. I. VIMP and SECM

“…Considering the signals C g ,A g , C H /A H and C ORR we can apply a common scheme for the intensity of the signals based on theoretical models on the electrochemistry of redox‐active solids (Lovrić & Scholz, 1997, 1999; Oldham, 1998; Schröder et al, 2000). As previously discussed, the signals C H /A H can mainly be attributed to the oxidation of Fe(III) species; haematite in particular (Le Formal et al, 2010, Cummings et al, 2011, 2012; Doménech‐Carbó et al, 2021; Klahr & Hamman, 2014) overlapped with the catalysed OER. The intensity of the C H peak will be representative of the net amount of such Fe(III) species (as well as their shape and size distribution and crystallinity).…”

“…That which appears in both negative‐ and positive‐going potential scan voltammograms at ~0.8 V can be associated (at least mainly) with the oxidation of haematite (C H , A H ), as judged by the similarity of the voltammetric response to that of clay bodies and haematites. The oxidation process can be represented as follows (Doménech‐Carbó et al, 2022): As previously noted, both OER and ORR processes can be catalysed by some of the components of the sample, haematite in particular. This compound is a recognized catalyst and photocatalyst for the OER process (Bouhjar et al, 2018; Peter, 2013; Shimizu, Sepunaru, & Compton, 2016; Shimizu, Tschulik, & Compton, 2016; Wan et al, 2019; Zhu et al, 2013), a role conceivably played by other Fe(III) minerals.…”

“…This compound is a recognized catalyst and photocatalyst for the OER process (Bouhjar et al, 2018; Peter, 2013; Shimizu, Sepunaru, & Compton, 2016; Shimizu, Tschulik, & Compton, 2016; Wan et al, 2019; Zhu et al, 2013), a role conceivably played by other Fe(III) minerals. In turn, the A H /C H signals can be attributed to the oxidation of haematite to higher oxidation states of iron (IV, V and VI) (Cummings et al, 2011, 2012; Doménech‐Carbó et al, 2021; Klahr & Hamman, 2014; Le Formal et al, 2010).…”

“…How to cite this article: Doménech-Carb o, A., Giannuzzi, M., Mangone, A., & Giannossa, L. C. (2022). Electrochemical methods to discriminate technology and provenance of Apulian red-figured pottery.…”

Electrochemical methods to discriminate technology and provenance of Apulian red‐figured pottery. II: EIS

“…In the current work, we have studied ceramic clay bodies using the Fe (CN) 6 3− /Fe (CN) 6 4− couple as the redox probe in order to avoid possible complications associated to the catalytic effects of some components (hematite in particular) on the oxygen reduction reaction process (Shimizu et al, 2016; Wan et al, 2019; Zhu et al, 2013). Because these effects focused our VIMP study of the same sample (Doménech‐Carbó et al, 2022), the acquisition of complementary information required the use of another redox probe for impedance measurements.…”