1 Electronic Supplementary Information for Experimental and Theoretical Insight into Electrocatalytic Hydrogen Evolution with Nickel bis-aryldithiolene Complexes as Catalysts Athanasios Zarkadoulas 1 , Martin J. Field 2 , Constantina Papatriantafyllopoulou 3 , Jennifer Fize 4 , Vincent Artero 4 *, Christiana A. Mitsopoulou 1 * 1 Inorganic Chemistry Laboratory, Chemistry Department, National and Kapodistrian University of Athens, Panepistimiopolis, Zografou 157 71, Greece 2 DYNAMO/DYNAMOP, Institut de Biologie Structurale, UMR CNRS/Université Grenoble Alpes/CEA 5075, EPN Campus, 6 rue Jules Horowitz F-38000 Grenoble, France 3 Department of Chemistry, University of Cyprus, 1678 Nicosia, Cyprus 4 Laboratory of Chemistry and Biology of Metals, Université Grenoble Alpes, CNRS, CEA, 17 rue des Martyrs, F-38000 Grenoble, France Corresponding author. Tel.: +30 210 7274452; fax: +30 210 7274435. E-mail address: cmitsop@chem.uoa.gr (C.A. Mitsopoulou), vincent.artero@cea.fr (V. Artero Table of contents Figure S1. CV of 2 in the presence of TFA…………………………………………...3 Figure S2. CV of 3 in the presence of TFA…………………………………………...4 Figure S3. CV of neat TFA in DMF…………………………………………………..5 Figure S4. Linear fit of Ep vs log[TFA]………………………………………...……..6 Figure S5. Linear sweep voltammetry for 1 and 2 with 10 mM TFA…………………7 Figure S6. Rinse tests for catalyst 1…………………………….……………………..8 Figure S7. DFT-calculated structure for intermediate [1(NiH)] 2- ……………………..9 Equation S1 for the calculation of the overpotentials………………………………..10 Scheme S1. Proposed mechanism for hydrogen evolution with catalyst 2…………..11 Table S1. Bond lengths for 2…………………………………………………………12 Table S2. Bond angles for 2………………………………………………………….14