Citation: Bunge, L.; Silva, H.G.; Cruz, P.L.; Iten, M. Testing of a Low-Cost Dry Cell Prototype for Oxyhydrogen Production. Designs 2022, 6, 79. https://doi.org/10.3390/ designs6050079 Academic Editor: Quanqing Yu Received: 18 July 2022 Accepted: 1 September 2022 Published: 7 September 2022 Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affil- iations. Copyright: © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Article Testing of a Low-Cost Dry Cell Prototype for Oxyhydrogen Production Lisa Bunge 1 , Hugo G. Silva 2,3, * , Pedro L. Cruz 4 and Muriel Iten 4 1 Cátedra de Energias Renováveis, Departamento de Eng. Mecatrónica, Universidade de Évora, Rua Romão Ramalho 59, 7000-671 Évora, Portugal 2 Laboratório Associado de Energia, Transporte e Aeronáutica (LAETA), Departamento de Física, ECT, Universidade de Évora, Rua Romão Ramalho 59, 7000-671 Évora, Portugal 3 INEGI Alentejo, Universidade de Évora, Largo dos Colegiais 2, 7000-803 Évora, Portugal 4 Low Carbon & Resource Efficiency, R & Di, Instituto de Soldadura e Qualidade, 4415-491 Grijó, Portugal * Correspondence: hgsilva@uevora.pt; Tel.: +351-967-480-736 Abstract: This work aims to study the production of oxyhydrogen gas by a small low-cost prototype consisting of six dry cells. Firstly, a molecular composition study of the gas was carried out, presenting concentrations of 67% H 2 and 28% O 2 . The deviation from the stoichiometric yield is discussed to be caused by water vapor production and/or oxygen dissolution in the liquid phase. Secondly, an efficiency study was done, considering the ratio between the reversible voltage of an electrolytic cell and the voltage applied to the dry cell by an external power source. Different working conditions (electrolyte concentration, 3% (w/w) of KHO and 20% (w/w) of KHO) have been tested to analyze their effect on the efficiency of the system. The results show that a lower electrolyte concentration increases the applied cell voltage, and so the necessary power input for gas production to occur, resulting in lower cell efficiency. Overall, the efficiencies are below 69.8 ± 0.6% for the studied electrolyte concentrations and approach approximately the same value around 50% for higher powers. Keywords: oxyhydrogen production; low-cost prototype; oxyhydrogen molecular composition; dry cell efficiency 1. Introduction Molecular hydrogen (H 2 ) can be used as fuel for energy production and is considered a secondary energy vector, since it does not exist in its pure form in nature. Hydrogen can be obtained through various processes and from various sources, including through the reformation of natural gas or biofuels; gasification of biomass and coal; electrolysis of water or water vapor at high temperatures; thermochemical cycles; and photocatalytic processes [1]. Hydrolysis is any chemical reaction in which water molecules break down one or more of their chemical bonds. Electrolysis, in turn, consists of separating water into hydrogen (H 2 ) and oxygen (O 2 ) using electrical energy [2], and occurs in electrolytic cells. This process has an efficiency as high as 85%, however, the amount of electricity required makes the overall process inefficient and often expensive [1]. Electrolysis is commonly made with the use of wet cells, which have two electrodes, an anode, and a cathode, made from some inert metals, such as platinum and stainless steel, or graphite. The electrodes are immersed in a water solution with an acid or a base, forming an electrolyte, in order to increase the electrical conductivity of the solution. This aims to reduce the enormous amount of energy required to perform the electrolysis of pure water, since it is not a good electrical conductor [2]. The electrolyte, when dissolved in water, results in a solution capable of conducting electricity. The electrolyte dissociates into cations and anions, with cations attracted by the negative pole and anions by the positive pole of the electrolytic cell. This allows the continuous flow of electricity, increasing the conductivity of Designs 2022, 6, 79. https://doi.org/10.3390/designs6050079 https://www.mdpi.com/journal/designs