Carbon-free fuel, also known as hydrogen fuel, is one of the modern sustainable energy sources. The two largest consumers of hydrogen fuel are the petroleum and fertilizer industries, which require around 50% and 37% of all the H2 generated. So the demand for H2 production has risen by 6% over the previous 5 years. One of the best renewable available technologies to generate H2 is from microbial electrolytic cells (MECs). With hydrogen, there are several byproducts of MECs like clean water, ethanol, methane, H2O2, etc. However MEC technologies are still in the early stages of development and need to be optimized to become the more advanced technology of the future. In this book chapter, the majority of the data cover various fermentative H2 generation methods from wastewater, various processes of scaling up of MECs, and recent advancements and applications of MECs in various fields.