An electrochemical detection of free chlorine using carbon‐metal (C−M) composite powder, with a nickel‐metal nanoparticle combined with a multilayered graphene nanoshell (Ni metal@multilayered graphene) as the main component, synthesized from CH4 via multimode microwave‐assisted catalytic decomposition, was studied. Morphological analysis of the C−M composite powder was performed by TEM–EDX and Raman spectroscopy. The C−M composite powder was packed in a porous microelectrode (PME), and its electrochemical activity with respect to free chlorine was evaluated using a potential sweep method. The C−M composite powder exhibited a sufficient activity against free chlorine. A current based on the reduction of free chlorine was observed in the potential < around+0.3 V vs. Ag/AgCl. A linear relationship was observed between the current and the concentration.

This cover picture presents new carbon‐metal composite particles; the nickel metal nanoparticles combined with a multilayered graphene nanoshell (Ni metal@multilayered graphene), which was synthesized from CH4 via multimode microwave‐assisted catalytic decomposition, were packed in a porous microelectrode (PME). Further, its electrode behavior with respect to free chlorine (hypochlorous acid (HOCl) and hypochlorite ions (OCl−)) has also been investigated. More details have been presented in the article by Fumihiro Kodera, Ryou Saito, Hiroya Ishikawa, Akihiko Miyakoshi, and Minoru Umeda. Please see DOI: 10.1002/elan.201800326.