Hydrogen evolution catalysis by terminal molybdenum-oxo complexes

Abstract

Summary Stable complexes with terminal triply bound metal-oxygen bonds are usually not considered as valuable catalysts for the hydrogen evolution reaction (HER). We now report the preparation of three conceptually different (oxo)molybdenum(V) corroles for testing if proton-assisted 2-electron reduction will lead to hyper-reactive molybdenum(III) capable of converting protons to hydrogen gas. The upto 670 mV differences in the [(oxo)Mo(IV)] - /[(oxo)Mo(III)] −2 redox potentials of the dissolved complexes came into effect by the catalytic onset potential for proton reduction thereby, significantly earlier than their reduction process in the absence of acids, but the two more promising complexes were not stable at practical conditions. Under heterogeneous conditions, the smallest and most electron-withdrawing catalyst did excel by all relevant criteria, including a 97% Faradaic efficiency for catalyzing HER from acidic water. This suggests complexes based on molybdenum, the only sustainable heavy transition metal, as catalysts for other yet unexplored green-energy-relevant processes.

Orthogonal Design of Fe−N4 Active Sites and Hierarchical Porosity in Hydrazine Oxidation Electrocatalysts

“…The contracted and tri-(rather than di-) anionic N 4 coordination core of corroles induces unusual reactivity and stability at the low and high oxidation state, respectively. [40,41] The redox potentials of metallocorroles are easily tuned by the nature of substituents at the meso-C position and via selective postfunctionalization. [42,43] Moreover, metallocorroles are extremely stable towards hydrolysis, and show a much reduced tendency of forming inactive μ-oxo-bridged bis-iron complexes.…”

“…An exciting new family of Fe−N 4 electrocatalysts is the family of metallocorroles, which have already been used for electrocatalyzing both reduction (of protons, oxygen, and CO 2 ) [34–36] and oxidation (hydroxide and water) [37–39] half‐cell reactions. The contracted and tri‐ (rather than di‐) anionic N 4 coordination core of corroles induces unusual reactivity and stability at the low and high oxidation state, respectively [40,41] . The redox potentials of metallocorroles are easily tuned by the nature of substituents at the meso ‐C position and via selective postfunctionalization [42,43] .…”

Electrocatalytic hydrogen production by CN– substituted cobalt triaryl corroles

“…35 The meso-CF 3 substituted molybdenum corrole displays more outstanding HER productivity and positive potential than the meso-C 6 F 5 one. 33 Cobalt corroles with phosphonic and carboxyl acid pendants functioning as protondonors improve HER activity. 36 Previously, we have used ethoxycarbonyl, 37 nitro, 38 amino, 39 aldehyde and amide pyridyl group 40 substituted cobalt corroles and free-base bis-corrole in the HER.…”

“…29 In 2014, Gross 30 firstly used cobalt trispentafluorophenyl corrole in the electrocatalytic HER. Copper, 31 iron 32 and molybdenum 33 corroles have also been applied as HER catalysts. It is found that the substitution of electron withdrawing or donating groups at the meso - or β-position would affect the redox potentials and significantly influence the ability of the complex to act as an electrocatalyst in the reduction.…”

“…35 The meso -CF 3 substituted molybdenum corrole displays more outstanding HER productivity and positive potential than the meso -C 6 F 5 one. 33 Cobalt corroles with phosphonic and carboxyl acid pendants functioning as proton-donors improve HER activity. 36…”