Efficient Light-Driven Hydrogen Evolution Using a Thiosemicarbazone-Nickel (II) Complex

ORIGINAL RESEARCH published: 27 June 2019 doi: 10.3389/fchem.2019.00405 Efficient Light-Driven Hydrogen Evolution Using a Thiosemicarbazone-Nickel (II) Complex Stylianos Panagiotakis 1 , Georgios Landrou 1 , Vasilis Nikolaou 1 , Anisa Putri 2 , Renaud Hardré 2 , Julien Massin 2 , Georgios Charalambidis 1*, Athanassios G. Coutsolelos 1* and Maylis Orio 2* 1 Laboratory of Bioinorganic Chemistry, Department of Chemistry, University of Crete, Heraklion, Greece, 2 Aix Marseille Université, CNRS, Centrale Marseille, iSm2, Marseille, France Edited by: Bunsho Ohtani, Hokkaido University, Japan Reviewed by: Marco Armandi, Polytechnic University of Turin, Italy Mirco Natali, University of Ferrara, Italy *Correspondence: Georgios Charalambidis Athanassios G. Coutsolelos Maylis Orio Specialty section: This article was submitted to Catalysis and Photocatalysis, a section of the journal Frontiers in Chemistry Received: 17 December 2018 Accepted: 20 May 2019 Published: 27 June 2019 Citation: Panagiotakis S, Landrou G, Nikolaou V, Putri A, Hardré R, Massin J, Charalambidis G, Coutsolelos AG and Orio M (2019) Efficient Light-Driven Hydrogen Evolution Using a Thiosemicarbazone-Nickel (II) Complex. Front. Chem. 7:405. doi: 10.3389/fchem.2019.00405 Frontiers in Chemistry | www.frontiersin.org In the following work, we carried out a systematic study investigating the behavior of a thiosemicarbazone-nickel (II) complex (NiTSC-OMe) as a molecular catalyst for photo-induced hydrogen production. A comprehensive comparison regarding the combination of three different chromophores with this catalyst has been performed, using [Ir(ppy)2 (bpy)]PF6 , [Ru(bpy)3 ]Cl2 and [ZnTMePy]PCl4 as photosensitizers. Thorough evaluation of the parameters affecting the hydrogen evolution experiments (i.e., concentration, pH, solvent nature, and ratio), has been performed in order to probe the most efficient photocatalytic system, which was comprised by NiTSC-OMe and [Ir(ppy)2 (bpy)]PF6 as catalyst and chromophore, respectively. The electrochemical together with the photophysical investigation clarified the properties of this photocatalytic system and allowed us to propose a possible reaction mechanism for hydrogen production. Keywords: light-driven hydrogen production, catalyst, nickel, molecular photosensitizer, photophysics INTRODUCTION One of the most important challenges of our society, that still lie ahead, is to discover renewable and abundant energy sources (Hosenuzzaman et al., 2015; Hosseini and Wahid, 2016). Solar energy is indeed an attractive and unlimited energy source which nonetheless requires the development of novel as well as efficient storage technologies (Styring, 2012; Tachibana et al., 2012; Faunce et al., 2013). Interestingly, hydrogen could unquestionably be applied for such a purpose: (i) it is the simplest and the most plentiful element on earth, (ii) the energy of the hydrogen-hydrogen bond is high, and (iii) it is considered as a non-polluting fuel (Peel, 2003). Hence, photocatalytic water splitting leading to hydrogen production is a method that without any doubt could be proved as an auspicious solution (Lewis and Nocera, 2006). Photocatalytic hydrogen production can be accomplished by systems containing a photosensitizer, a sacrificial electron donor and a catalyst (Ladomenou et al., 2015; Yuan et al., 2017). Nevertheless, there are plenty unsolved issues that still rest in the field of photocatalytic hydrogen production. Specifically, the development of systems utilizing earth-abundant materials with enhanced efficiency and durability (Wang and Sun, 2010; Du and Eisenberg, 2012). To that end, numerous hydrogen evolution catalysts along with a great number of different photosensitizers have been extensively examined over the last years (Tran et al., 2010, 2012; Du and Eisenberg, 2012; Wang et al., 2012; Sartorel et al., 2013). 1 June 2019 | Volume 7 | Article 405 Panagiotakis et al. Light-Driven Hydrogen Evolution Reaction solvent ratio, and the influence of pH in the buffer solution. The electron transfer processes that occur were examined through fluorescence spectroscopic techniques. To solidify the photochemical stability of our system, regeneration experiments were conducted and the homogeneous nature of our catalytic system was proved using poisoning experiments. Based on the results gathered from these studies we were finally able to propose a possible reaction mechanism for light-driven hydrogen production with our photocatalytic system. Photocatalytic systems involving low-cost molecular catalysts and compounds prepared through easy synthetic approaches have been widely studied over the past decade (Artero et al., 2011; Eckenhoff et al., 2013; Ladomenou et al., 2015). Specifically, cobaloximes (Fihri et al., 2008; Lazarides et al., 2009, 2014; Du and Eisenberg, 2012; Landrou et al., 2016; Panagiotopoulos et al., 2016), and other polypyridine cobalt complexes have been applied as noble-metal-free catalysts (Eckenhoff et al., 2013; Yin et al., 2015; Zee et al., 2015). Although, several of these catalysts are efficient for photocatalytic hydrogen evolution reaction (HER), their stability was greatly limited upon visible light irradiation. Moreover, many researches draw inspiration from Nature trying to replicate the function of the hydrogenase enzymes (Lubitz et al., 2014; Brazzolotto et al., 2016), leading to the design of nickel complexes that were evaluated as molecular catalysts for HER. As a result, plenty nickel catalysts such as nickel bis(diphosphine) (DuBois and DuBois, 2009a,b; Helm et al., 2011; McLaughlin et al., 2011), and pyridinethiolate (Han et al., 2012, 2013; Rao et al., 2016) have been applied in such schemes, since they reproduce the structure of the active site of hydrogenase. Due to the effect of non-innocent ligands, (Han et al., 2012, 2013; Rao et al., 2015, 2016; Inoue et al., 2017) such nickel complexes have displayed excellent efficiency as catalyst reaching around 7,500 TON (Han et al., 2013; Rao et al., 2016). Thiosemicarbazone metal complexes are an emerging class of new HER electrocatalysts (Haddad et al., 2016, 2017; Straistari et al., 2017, 2018a,b) that have already been proved to be redox active (Blanchard et al., 2005; Haddad et al., 2017; Straistari et al., 2017) The presence of S-donors as well as N-atoms in thiosemicarbazone allows the protonation of the ligand and serve as proton relays (Campbell, 1975; DuBois, 2014; Coutard et al., 2016). One of the most essential aspect of light-driven proton reduction is the appropriate choice of the light-harvesting unit (i.e., photosensitizer, Ps). Despite the fact that [Ru(bpy)3 ]Cl2 remains the most widely employed chromophore in such systems (Khnayzer et al., 2014; Lo et al., 2016), iridium complexes are still the most efficient entities found in several photocatalytic systems (Goldsmith et al., 2005; Andreiadis et al., 2011). Additionally, porphyrins and other tetrapyrrolic deriv (...truncated)