Progress of oxygen and hydrogen evolution reactions in parallel with chlorine evolution on manganese single-atom catalysts based on perfect and defective porphyrin, corrole, and phthalocyanine Nasimeh Lari Dashti, Afshan Mohajeri * Department of Chemistry, College of Sciences, Shiraz University, Shiraz 7194684795, Iran highlights graphical abstract  Catalytic behaviors of four coordi- nated N4 templates for O 2 ,H 2 , and Cl 2 evolutions are investigated.  Porphyrin, corrole, and phthalocy- anine incorporating Mn single atom are examined.  The impact of defect around Mn eN4 active site on the catalytic activity is focused.  The O 2 evolution is slightly hin- dered by OCl formation on the same OER active sites.  The water oxidation can be enhanced with small increases in pH value. article info Article history: Received 1 July 2022 Received in revised form 6 October 2022 Accepted 12 October 2022 Available online xxx Keywords: Single atom catalyst Water splitting abstract During the seawater electrolysis, besides the hydrogen evolution reaction (HER) at the cathode, there is always debate on the simultaneous occurrence of chlorine evolution re- action (CER) and oxygen evolution reaction (OER) at the anode. In this context, the selec- tivity toward anodic reactions is a challenge and could be adjusted through the variation of the electronic structure of the electrocatalyst. The present study aims to investigate the electrocatalytic behavior of four coordinated square-planar N4 templates toward parallel evolution of oxygen and chlorine at the anode as well as hydrogen evolution at the cath- ode. To this end, our focus will be on porphyrin, corrole, and phthalocyanine substrates incorporating Mn single atom highlighting the impact of perturbations around the MneN4 active site on the catalytic activity of these substrates. Accordingly, the reactivity and selectivity of 21 perfect and defective substrates toward the OER, CER, and HER have been * Corresponding author. E-mail address: amohajeri@shirazu.ac.ir (A. Mohajeri). Available online at www.sciencedirect.com ScienceDirect journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy xxx (xxxx) xxx https://doi.org/10.1016/j.ijhydene.2022.10.111 0360-3199/© 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved. Please cite this article as: Dashti NL, Mohajeri A, Progress of oxygen and hydrogen evolution reactions in parallel with chlorine evolution on manganese single-atom catalysts based on perfect and defective porphyrin, corrole, and phthalocyanine, International Journal of Hydrogen Energy, https://doi.org/10.1016/j.ijhydene.2022.10.111