O.Cuzan-Munteanu, D.Sirbu, M.Giorgi, S.Shova, E.A.Gibson, M.Réglier, M.Orio, L.Martins, A.Benniston

 Eur. J. Inorg. Chem., 2020: 813-822

Three neutral palladium(II) complexes were synthesized and characterized by several spectroscopic methods, ESI mass spectrometry and single‐crystal X‐ray diffraction. The geometry around the palladium(II) centre for each complex is described as distorted square planar. The complexes were tested as potential catalysts for electrochemical proton reduction in DMF using trifluoroacetic acid (TFA). Gas analysis under electrocatalytic conditions at a boron‐doped diamond working electrode confirmed the hydrogen production. After performing similar gas analysis experiments using a working mercury pool electrode, no hydrogen was detected which supports the concept that the active species of the catalytic process are palladium particles formed on the surface of the working electrode. The palladium(II) benzotriazolyl phenolate complexes facilitate the formation of particles for electrocatalytic hydrogen production. Furthermore, the palladium(II) complexes PdL2 and PdL3 were able to catalyse microwave‐assisted Heck and Sonogashira C–C coupling reactions.

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E.Giannoudis, E.Benazzi, J.K.G.Karlsson, G.Copley, S.Panagiotakis, G.Landrou, P.Angaridis, V.Nikolaou, C.Matthaiaki, G. Charalambidis, E.A.Gibson, A.G.Coutsolelos

Inorg. Chem. 2020, 59, 3, 1611–1621

We report a comparison between a series of zinc and tin porphyrins as photosensitizers for photochemical hydrogen evolution using cobaloxime complexes as molecular catalysts. Among all the chromophores tested, only the positively charged zinc porphyrin, [ZnTMePyP⁴⁺]Cl₄, and the neutral tin porphyrin derivatives, Sn(OH)₂TPyP, Sn(Cl₂)TPP-[COOMe]₄, and Sn(Cl₂)TPP-[PO(OEt)₂]₄, were photocatalytically active. Hydrogen evolution was strongly affected by the pH value as well as the different concentrations of both the sensitizer and the catalyst. A comprehensive photophysical and electrochemical investigation was conducted in order to examine the mechanism of photocatalysis. The results derived from this study establish fundamental criteria with respect to the design and synthesis of porphyrin derivatives for their application as photosensitizers in photoinduced hydrogen evolution.

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M.T.Pryce, A.A.Cullen, L.O'Reilly, K.Heintz, C.Long, A.Heise, R.Murphy, E.A.Gibson, J.K.G.Karlsson, M.Towrie, and G.Greetham

Front.Chem., 2020,8,957

A novel 4,4-difuoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) copolymer with diethynylbenzene has been synthesised, and its ability to act as a photosensitiser for the photocatalytic generation of hydrogen was investigated by time-resolved spectroscopic techniques spanning the ps- to ns-timescales. Both transient absorption and time-resolved infrared spectroscopy were used to probe the excited state dynamics of this photosensitising unit in a variety of solvents. These studies indicated how environmental factors can influence the photophysics of the BODIPY polymer. A homogeneous photocatalytic hydrogen evolution system has been developed using the BODIPY copolymer and cobaloxime which provides hydrogen evolution rates of 319 μmol h−1 g−1 after 24 h of visible irradiation.

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M.Zannotti, E.Benazzi, L.A.Stevens, L.Bruce, M.Minicucci, C.E.Snape, E.A.Gibson, R.Giovannetti

Reduced graphene oxide (rGO) and NiO/rGO photocathodes were built and analysed, investigating different amounts of rGO material. A detailed characterization of NiO/rGO films was carried out by SEM, Raman, and surface analysis. BET analysis revealed that the optimum surface area of the films was between 0.0 and 0.3 mg of rGO, while the surface area was lower with increasing graphene content. The p-type dye-sensitized solar cells prepared from these films showing an efficiency almost 2 times higher with respect to the solar cell with NiO alone. An EIS study showed that the charge recombination resistance was lower in the presence of the rGO, but the hole lifetime was similar. This behavior suggests that the higher JSC obtained with the higher amount of rGO can be ascribed to the higher dye uptake, which leads to a higher concentration of holes in the photocathodes.

ACS Appl. Energy Mater. 2019, 2, 10, 7345–7353

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N.Põldme,   L.O'Reilly,   I.Fletcher,   J.Portoles,   I.V. Sazanovich,   M.Towrie,   C.Long,   J.G. Vos,   M.T. Pryce  and  E.A. Gibson 

Chem. Sci., 2019,10, 99-112

A new approach to increasing the faradaic efficiency of dye-sensitised photocathodes for H₂ evolution from water, using integrated photocatalysts furnished with ester groups on the peripheral ligands, is described.

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E.Benazzi, J.Mallows, G.H. Summers, F.A. Black and E.A. Gibson 

J. Mater. Chem. C, 2019,7, 10409-10445

Dye-sensitized solar cells are photoelectrochemical devices, which are of great interest due to their ease of fabrication and attractive design. This review details the progress made over the last 20 years into the development of more efficient p-type DSCs with the goal of combining both p and the more widely studied n-type (TiO₂)-based photoelectrodes in tandem-DSCs. Such tandem architectures offer an opportunity to collect more light, more efficiently by overcoming the thermodynamic limits of single-junction devices. The main components of the p-DSCs, such as the variety of different sensitizers, p-type semiconductors and electrolytes are introduced and their typical performance in devices are compared. The kinetics of light-induced charge transfer at the interfaces between these materials are also discussed and suggestions are made as to which factors could be a priority for future research to increase the performance of p-type DSC to match state-of-the-art TiO₂-based devices, which is necessary for a step change in the conversion efficiency.

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A.Reddy, F.A.Black, J.Mallows, E.A.Gibson and J.Fielden

Dyes and Pigments,2019,165, 508-517

A family of six (five new) thiophenyl bridged triarylamine-donor based dyes with pyridine anchoring groups have been synthesized and studied as sensitizers for the p-type dye-sensitized solar cell. In all cases, compared to their dicyano counterparts, the pyridinium based dyes have higher extinction coefficients and smaller HOMO-LUMO gaps that give broader spectrum absorption.

Pyridiniums may provide a new, and easily accessible high performance acceptor for p-DSSC dyes, but are likely better paired with anionic binding groups such as carboxylates.

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A series of zinc tetraphenylporphyrin photosensitizers furnished with three different anchoring groups, benzoic acid, phenylphosphonate and coumarin-3-carboxylic acid, were prepared using ‘click’ methodology. All three gave modest performances in liquid junction devices with I₃^–/I^– as the electrolyte. The distinct spectroscopic properties of the porphyrins allowed a detailed investigation of the adsorption behaviour and kinetics for charge transfer at the NiO|porphyrin interface. The adsorption behaviour was modelled using the Langmuir isotherm model and the phosphonate anchoring group was found to have the highest affinity for NiO (6.65 × 10⁴M⁻¹) and the fastest rate of adsorption (2.46 × 10⁷cm²mol⁻¹min⁻¹). The photocurrent of the p-type dye-sensitized solar cells increased with increasing dye loading and corresponding light harvesting efficiency of the electrodes. Coordinating the zinc to a pyridyl-functionalized fullerene (C₆₀PPy) extended the charge-separated state lifetime from ca 200 ps to 4 ns and a positive improvement in the absorbed photon to current conversion efficiency was observed. Finally, we confirmed the viability of electron transfer from the appended C₆₀PPy to phenyl-C61-butyric acid methyl ester, a typical electron transporting layer in organic photovoltaics. This has implications for assembling efficient solid-state tandem solar cells in the future.

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A.Kolay,   N.T. Z. Potts,  K.Sardar,   E.A. Gibson  and  M.Deepa

Sustainable Energy Fuels, 2019,3, 514-528

A multifunctional tandem cell has been fashioned by (i) replacing the conventional counter electrode in a n-type titanium dioxide-based quantum dot sensitized solar cell (QDSC) with a QD-sensitized p-type nickel oxide photocathode to harness maximum power-conversion efficiency, and (ii) by coating an electrochromic molybdenum oxide overlayer at the photoanode.

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C.Hierlinger, H.V. Flint, D.B. Cordes, A.M.Z. Slawin, E.A. Gibson, D.Jacquemin, V.Guerchais, E.Zysman-Colman

Polyhedron, 2018,140,109-115

The synthesis of a new complex of the form [Ir(C^N^C)(N^N)Cl] [where C^N^C = 2-(bis(4-(tert-butyl)phenyl)methyl)pyridinato (dtBubnpy, L1) and N^N is diethyl [2,2′-bipyridine-4,4′-dicarboxylate (deeb)] was synthesized and tested. The photophysical and electrochemical properties suggest the use of this complex as a dye in dye-sensitized solar cells. 

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