The reduction of greenhouse gas emissions is one of the main issues of our time. Hydrogen is considered a promising candidate that is increasingly intended to replace fossil fuels. To cut down greenhouse gas emissions, it is essential that future hydrogen production is based on renewable energy sources. One such possibility is the electrolysis of water, provided it is operated with electricity from renewable energy sources. At present, however, only a very small proportion of global hydrogen is produced by means of electrolysis due to higher costs of production compared to fossil-based processes. Pure oxygen is produced as a by-product of water electrolysis, which is usually released into the environment without further use. Since oxygen is a gas that is used in many ways in industry and medicine, the present work investigates possible ways of utilizing by-product oxygen from electrolysis, whereby the overall efficiency of the electrolysis process should be improved and with the objective to keep water electrolysis competitive against conventional hydrogen production methods.