Photochemical Water Oxidation Catalyzed by a Water‐Soluble Copper Phthalocyanine Complex

Abstract

Copper tetrasulfonatophthalocyanine (CuPcTS) is reported to serve as a catalyst for photochemical water oxidation via a radical coupling mechanism. Chloride greatly inhibits the water oxidation rate as a result of axial chloride binding to CuPcTS, preventing formation of the Cu oxyl or hydroxyl intermediate required for O−O bond formation.

A Bio‐inspired Cu4O4 Cubane: Effective Molecular Catalysts for Electrocatalytic Water Oxidation in Aqueous Solution

“…Recrystallization of [(L Gly -Cu) 4 ] from acetonitrile/water solution gave rise to dark green blockshaped crystals.T he X-ray crystal structure revealed that [(L Gly -Cu) 4 ]( L Gly :3 -methoxy-salicylidene-glycine) featured au nique tetrameric cubane-like structure.A ss hown in Figure 1, each Cu atom is coordinated with one Na tom and five Oatoms.T aking Cu1 as arepresentative,the N1, O2, and O3 atoms from one horizontal ligand and the O2' atom from another vertical ligand are sited in the equatorial plane,while the O2'' and O1' atoms are arranged in an apical fashion. Thet urnover frequency (TOF) is determined to be 267 s À1 for [(L Gly -Cu) 4 ]at1.70 Vand 105 s À1 for [(L Glu -Cu) 4 ]at 1.56 V. Theexceptional catalytic efficiency, higher than those of mono-or binuclear ones (0.4-100 s À1 ) [11][12][13] enable us to believe that the Cu 4 O 4 cubane core is promising for the catalytic oxygen evolution. Indeed, the assynthesized cubane complexes ([(L Gly -Cu) 4 ]and [(L Glu -Cu) 4 ]) exhibit superior oxygen evolution ability in aqueous solution (pH 12).…”

“…Despite not fully elucidating these factors, there have been numerous advances in molecular catalyst design for water oxidation. [11][12][13] Their superior biomimetic reactivity [14] with oxygen, and the unique covalent metal-oxo bonding in Cu 2 (m-O) 2 core are expected to be advantage for oxygen evolution. [10] Owing to inexpensive and easily accessible to different oxidation state,c opper-based molecular water oxidation catalysts have been documented with the focus on mono-and bi-nuclear copper complexes.…”

“…[19] Thefitted slope is equal to ÀRT/anFand RT/(1Àa)nF for the cathodic peak (E p,c )and the anodic peak (E p,a ), where a (transfer coefficient) and n can be deduced as 0.5 and 2respectively (see details in the Supporting Information). [11][12][13] Thel inear scan voltammograms (LSVs) for [(L Gly -Cu) 4 ]a nd [(L Glu -Cu) 4 ]w ere further obtained at tindoped indium oxide (ITO) electrodes.T he greatly enhanced catalytic current suggested water oxidation occurrence (Supporting Information, Figure S9). Thep rofile of the differential pulse voltammetry (DPV) of [(L Gly -Cu) 4 ]w as dramatically changed by replacing the solvent from acetonitrile to PBS aqueous solution (pH 12; Supporting Information, Figures S7, S8).…”

“…Thep rofile of the differential pulse voltammetry (DPV) of [(L Gly -Cu) 4 ]w as dramatically changed by replacing the solvent from acetonitrile to PBS aqueous solution (pH 12; Supporting Information, Figures S7, S8). [11][12][13] To verify the oxygen evolution, controlled-potential electrolysis (CPE) of 0.25 mm [(L Gly -Cu) 4 ]i n0 .2 m PBS (pH 12.0) was performed in ag as-tight custom-designed cell at 1.50 Vw ith aI TO electrode (1.00 cm 2 ;S upporting Information, Figure S11). [11][12][13] Thel inear scan voltammograms (LSVs) for [(L Gly -Cu) 4 ]a nd [(L Glu -Cu) 4 ]w ere further obtained at tindoped indium oxide (ITO) electrodes.T he greatly enhanced catalytic current suggested water oxidation occurrence (Supporting Information, Figure S9).…”

“…Given that [(L Gly -Cu) 4 ]w as only soluble in alkaline solution, we utilized [(L Glu -Cu) 4 ]w ith good solubility in all pH range of aqueous solutions to further evaluate the pHdependence of the redox couples.A ss hown in the Pourbaix diagram (Supporting Information, Figure S19) [10][11][12], the signal of the highervalent redox couples overlapped with the water oxidation current, thus preventing accurate determination of the redox current of the possible intermediates in the Pourbaix diagram. To gain abetter understanding of the redox properties,aCV study was performed under acidic and weak basic conditions (pH [4][5][6][7][8][9], where the catalytic current was negligible.T he potential of Cu 4 III /Cu 2 III Cu 2 IV couples exhibited as lope of À49 mV/pH, in line with the 2e À /2 H + proton-coupled electron transfer (PCET) process (À59 mV/pH, Nernstian ideal).…”