Rationalizing In Situ Active Repair in Hydrogen Evolution Photocatalysis via Non‐Invasive Raman Spectroscopy

Abstract

Currently, most photosensitizers and catalysts used in the field of artificial photosynthesis are still based on rare earth metals and should thus be utilized as efficiently and economically as possible. While repair of an inactivated catalyst is a potential mitigation strategy, this remains a challenge. State‐of‐the‐art methods are crucial for characterizing reaction products during photocatalysis and repair, and are currently based on invasive analysis techniques limiting real‐time access to the involved mechanisms. Herein, we use an innovative in situ technique for detecting both initially evolved hydrogen and after active repair via advanced non‐invasive rotational Raman spectroscopy. This facilitates unprecedently accurate monitoring of gaseous reaction products and insight into the mechanism of active repair during light‐driven catalysts enabling the identification of relevant mechanistic details along with innovative repair strategies.

An Algebraic Blueprint for Predicting Turnover Numbers and Endpoints in Photocatalysis

“…Experimental data established via continuous Raman measurements using ([(tbbpy) 2 Ru(tpphz)PtI 2 ](PF 6 ) 2 (RuPtI 2 , with tbbpy = 4,4'-di-tert.-butyl-2,2'-bipyridine, tpphz = tetrapyrido[3,2-a:2',3'c:2'',3''-h:2''',3'''-j]phenazine and PF 6 À = hexafluorophosphate [21][22][23] was used for validating the derived approach. [24,25] At the beginning of the observation period of a catalytic process only the educts of the reaction are present.…”

“…Similar to the approach above (i. e., with the same boundary conditions) a second fit function for a differently behaving catalytic system was derived, i. e., for the photocatalytic behavior after repair of the catalyst RuPtI 2 (see Figure 1b; details about the repair procedure and mechanism of the catalyst can be found elsewhere [22,23] ), which does not show an induction period but rather a linear increase in photoproduct formation right at the start of the irradiation process. The first estimate based on the experimental data used the basic mathematical bounded growth function with barrier S described as:…”

Synthesis of Ru(ii) and Os(ii) photosensitizers bearing one 9,10-diamino-1,4,5,8-tetraazaphenanthrene scaffold

“…24,25 A common interest however, for many photosensitizers, earth abundant and rare, is the development of ligands with extended π-systems or with the ability to bridge a second metal center. [26][27][28][29][30][31][32][33][34][35][36][37][38] For example, in biomedical applications, intercala-tion within DNA or photoreaction with DNA bases was made possible with transition metal complexes (Ru, Rh, Os) carrying extended ligands such as TPPHZ (tetrapyrido[3,2-a:2′,3′-c:3″,2″h:2′′′,3′′′-j]phenazine), dppz (dipyrido[3,2-a:2′,3′-c]phenazine), PHEHAT (1,10-phenanthrolino [5,6-b]-1,4,5,8,9,12-hexaazatriphenylene) or TAPHAT (1,4,5,8-tetraazaphenanthrene[9,10-b]-1,4,5,8,9,12-hexaazatriphenylene). 27,[39][40][41][42][43] The structure of these ligands are presented in the ESI.…”

“…[52][53][54][55][56][57][58][59] The TPPHZ ligand has been extensively used in the field of hydrogen photoproduction with the development of photosensitizers such as [Ru(dtb) 2 (TPPHZ)MX 2 ] 2+ , where M is either Pt or Pd, X is Cl or I, and dtb is 4,4′-t Bu-2,2′-bipyridine. [35][36][37] Light excitation of these photosensitizers leads to an initial electron transfer from the Ru(II) centre to the bridging ligand, followed by the activation of the catalytic centre (M). The Ru(II) centre is usually regenerated by electron transfer from a sacrificial elec-tron donor reagent present in solution such as triethylamine or triethanolamine.…”