Water Electrolysis Accompanied by Side Reactions

Water electrolysis is used to teach important and fundamental concepts in chemistry. In practical water electrolysis experiments, it is difficult to achieve the ideal 2:1 ratio of hydrogen to oxygen. This work demonstrates an experimental setup comprising multiple water electrolysis cells connected in series to simultaneously visualize the effects of various electrode materials and electrolytes on water electrolysis. The volumes of oxygen were lower when using stainless steel and graphite anodes, which corrode in the electrolytes containing SO42– and NO3– anions, compared to those in the presence of the noncorroding Pt electrode. In addition, the volumes of hydrogen in the presence of NO3– anions, which are catalytically reduced on the cathodes of stainless steel and graphite, were remarkably lower than those obtained with the noncatalyzing Pt cathode. These phenomena are attributed to side reactions which consume portions of the electrons intended for water electrolysis. This demonstration can help students to realize that the experimental results of water electrolysis should be carefully interpreted as they may include a contribution from electrode side reactions.