Reactivity and Mechanism Studies of Hydrogen Evolution Catalyzed by Copper Corroles

Abstract

Several copper corrole complexes were synthesized, and their catalytic activities for hydrogen (H 2 ) evolution were examined. Our results showed that substituents at the meso positions of corrole macrocycles played significant roles in regulating the redox and thus the catalytic properties of copper corrole complexes: strong electron-withdrawing substituents can improve the catalysis for hydrogen evolution, while electron-donating substituents are not favored in this system. Copper complex of 5,15-pentafluorophenyl-10-(4-nitrophenyl)corrole (1) was shown to have the best electrocatalytic performance among copper corroles examined. Complex 1 can electrocatalyze H 2 evolution using trifluoroacetic acid (TFA) as the proton source in acetonitrile. In cyclic voltammetry, the value of i cat /i p = 303 (i cat is the catalytic current, i p is the one-electron peak current of 1 in the absence of acid) at scan rate 100 mV s −1 and 20 °C is remarkable. Electrochemical and spectroscopic measurements revealed that 1 has the desired stability in concentrated TFA acid solution and is unchanged by functioning as an electrocatalyst. Stopped-flow, spectroelectrochemistry and theoretical studies provided valuable insights into the mechanism of hydrogen evolution mediated by 1. Doubly reduced 1 is the catalytic active species that reacts with a proton to give the hydride intermediate for subsequent generation of H 2 .

Solar‐to‐Hydrogen Energy Conversion Based on Water Splitting

“…The bond strength of the formed MH should be neither too strong nor too weak to achieve the highest activity. [110][111][112][113][114][115] Pt group metals have proven to be the most efficient HER electrocatalysts theoretically and experimentally. However, if the MH bond is too weak, the charge density on the hydrogen atom will be low and the formation of the HH bond from the electrophilic attack by the second proton will be unfavorable.…”

Convenient Immobilization of Cobalt Corroles on Carbon Nanotubes through Covalent Bonds for Electrocatalytic Hydrogen and Oxygen Evolution Reactions

“…[1][2][3] During the last decade,avariety of molecular complexes based on earth-abundant transition-metal elements including Mn, [4][5][6][7] Fe, [8][9][10][11][12][13][14] Co, [15][16][17][18][19][20][21] Ni, [22][23][24][25][26][27][28] and Cu [29][30][31][32][33] have been identified as catalystsf or these two reactions. [1][2][3] During the last decade,avariety of molecular complexes based on earth-abundant transition-metal elements including Mn, [4][5][6][7] Fe, [8][9][10][11][12][13][14] Co, [15][16][17...…”

Antimony Complexes for Electrocatalysis: Activity of a Main‐Group Element in Proton Reduction

“…An additional irreversible peak appears upon addition of TFAthat increases as the acid concentration increases,w hich we attribute to proton-reduction catalysis. [11][12][13] To better understand the catalytic system, several control experiments were conducted, including measurements on blank electrolyte solutions (with TFA) and the free-base porphyrin TP in the presence of TFA. These control experiments explicitly demonstrate the involvement of the Sb center in the catalysis (Supporting Information, Figure S4A,B).…”

“…[24] Thea ctive catalyst I5 begins the catalytic cycle by accepting ap roton with its 5s lone pair, forming the Sb V À H hydride intermediate I6.T he formation of I6 is practically isoergonic (+ 0.2 kcal mol À1 ), with an activation free energy of 9.3 kcal mol À1 .T his intermediate finds many analogues in various metal hydride species,o ccurring as intermediates in proton reduction catalysis. [11][12][13] Thec alculated Sb À Hb ond length in I6 is 1.70 ,a nd the calculated charge of the Hi s À0.24 e, based on an atomic polar tensor charge analysis.The reduction of I6 requires 11.7 kcal mol À1 .Like I2,the incoming electron populates the porphyrin ring rather than the metal center, because the two axial ligands obstruct the formation of an Sb lone pair. Protonation of the reduced hydride I7 [25] forms the H 2 -bound complex I8 with afree energy change of + 3.2 kcal mol À1 and an activation free energy of 16.2 kcal mol À1 .T he HÀHb ond length in I8 is 0.76 ,w hich is very similar to an isolated H 2 molecule.O nt he other hand, the distance between Sb and H 2 is about 3.3 ,i ndicating av ery Figure 3.…”