Towards win-win electrochemical alternative for depolluting water and producing green H2: Understanding and unrevealing the participation of sacrificial organic compound on H2 production

Author(s)

dos Santos, Elisama Vieira ; Cardozo, Jussara Camara ; Zambrano, Tabata Natasha Feijoo ; Alfaro, Marco Antonio Quiroz ; Martinez-Huitle, Carlos A.

• Document type: Journal article
• Source: INTERNATIONAL JOURNAL OF HYDROGEN ENERGY; v. 110, p. 11-pg., 2024-03-18.

Abstract

In the field of electrochemical research, two topics stand out for the importance of their results: the degradation of biorefractory organic compounds and the direct or indirect production of clean and renewable energy. The first focus involves effectively removing pollutants from wastewater, whether sourced from urban or industrial activities. The second aims to harness electrochemical processes to advance efficient energy sources that contribute to the decarbonization of the economy. Within this framework, this research investigates an experimental approach that connects these objectives sustainably and efficiently. For this purpose, a doublecompartment electrochemical cell was set up, separated by a Nafion(R) membrane, with a maximum interelectrode distance of 3 cm. The anode compartment (0.02 L capacity) contained a solution of 0.25 M H2SO4 + 50 ppm of Olanzapine (OL), which was passed through the cell at a rate of 10 mL min-1 towards a 1 L external reservoir. The electrochemical oxidation (EO) experiments (30 mA cm-2 and 25 degrees C) were performed with selected anodic materials such as boron-doped diamond (BDD), PbO2-F, Pt and Ru-Ir (DSA). Meanwhile, the cathodic compartment (0.04 L) was also maintained at 25 degrees C, contained 0.25 M H2SO4 as supporting electrolyte and a nickel-iron (Ni-Fe) stainless steel (SS) mesh as cathode material. Composition analysis of the OL solution was carried out from the external reservoir, while the volume of hydrogen (VH2) produced at the cathode was measured in-situ with an inverted burette system, while a solar photovoltaic (PV) system was used to power the entire electrochemical setup. Results indicated that BDD and PbO2-F anodes effectively oxidized OL, achieving a total current efficiency (TCE, in %) greater than 50%, whereas Pt and Ru-Ir anodes showed lower TCEs. Similarly, energy consumption of about 30 kWh L-1 for BDD and PbO2-F were achieved, compared to over 140 kWh L1 for Ru-Ir. On the other hand, the simultaneous measurement of cell potential and H2 volume produced were performed as a function of the electrolysis time for each one of the materials used as anodes. While the variation of the V(H2) produced with electrolysis time initially suggests a dependence on the nature of the anode material, this is somewhat misleading. For all anodes, there is a linear relationship between electrolysis time and H2 production when the data is shown per unit of applied current. The remarkable part arises when we analyze the correlation between the amount of OL oxidized and the amount of H2 produced, demonstrating that two sources of protons (H+) contribute to H2 gas formation at the cathode. It is proven that, at a constant current intensity and a given electrolysis time, the amount of H2 formed is the same for each anode; however, the proportion of protons (H+) sourced from each contributor varies. For BDD electrodes, more than 40% of the protons needed for H2 production are coming from OL, whereas DSA (Ru-Ir) anodes contribute just over 7%. This makes production costs lower using BDD anodes for OL oxidation (3.4 USD/kg H2), than with DSA electrodes (5.9 USD/kg H2). Therefore, it is our conviction that this experimental alternative represents an efficient and sustainable proposal, worthy of consideration. (AU)

• FAPESP's process: 19/13113-4 - Photo (electro) catalysis and photoelectro-fenton processes for emerging contaminants removal from industrial wastewater
• Grantee: Maria Valnice Boldrin
• Support Opportunities: Regular Research Grants
• FAPESP's process: 14/50945-4 - INCT 2014: National Institute for Alternative Technologies of Detection, Toxicological Evaluation and Removal of Micropollutants and Radioactivies
• Grantee: Maria Valnice Boldrin
• Support Opportunities: Research Projects - Thematic Grants