Iron compounds from Euterpe oleracea Mart (açai) seed ash as electrocatalyst for oxygen evolution reaction

The production of pulp from Euterpe oleracea Mart. palm fruits (açaí) generates a significant amount of primary solid waste, whose inadequate disposal poses environmental risks. The açaí seeds ash contains iron compounds and was used as an electrocatalyst in the oxygen evolution reaction (OER) process. The ashes were obtained by calcination of açaí seeds. The samples were characterized by several techniques, including XRF, XRD, TEM, FTIR, Mössbauer and magnetometry. The Mössbauer results revealed the presence of metal iron (α-Fe) and magnetite (Fe₃O₄). The electrochemical evaluation demonstrated that açaí seeds ash had promising catalytic activity for OER, exhibiting an overpotential of 349 mV at 10 mA cm⁻². The analysis of the Tafel curve indicated a superior electron transfer kinetics of 61 mV dec⁻¹, and the chronopotentiometry tests for 16 h showed electrochemical stability. The catalytic performance was attributed to the biochar composition, rich in iron in several oxidation states, which facilitates the charge transfer. These results suggested that açaí seed ash can be a valuable source for the development of efficient electrocatalysts for OER, contributing to the production of hydrogen and the circular economy.