Electrocatalytic H<sub>2</sub> evolution promoted by a bioinspired (N2S2)Ni(<scp>ii</scp>) complex

Sinha, Soumalya; Tran, Giang N.; Na, Hanah; Mirica, Liviu M.

doi:10.1039/d1cc05139c

“…Recently, our group has shown that the N2S2 ligand, the dithioether analog of the N4 pyridinophane, stabilizes Pd I complexes 29 and catalyzes HER via a Ni 0/II cycle 30 . We also reported that R N3C-type ligands allowed the stabilization of high-valent Ni centers 31 – 34 .…”

Section: Resultsmentioning

confidence: 99%

Characterization of paramagnetic states in an organometallic nickel hydrogen evolution electrocatalyst

Chakrabarti

¹

,

Sinha

²

,

Tran

³

et al. 2023

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Significant progress has been made in the bioinorganic modeling of the paramagnetic states believed to be involved in the hydrogen redox chemistry catalyzed by [NiFe] hydrogenase. However, the characterization and isolation of intermediates involved in mononuclear Ni electrocatalysts which are reported to operate through a NiI/III cycle have largely remained elusive. Herein, we report a NiII complex (NCHS2)Ni(OTf)2, where NCHS2 is 3,7-dithia-1(2,6)-pyridina-5(1,3)-benzenacyclooctaphane, that is an efficient electrocatalyst for the hydrogen evolution reaction (HER) with turnover frequencies of ~3,000 s−1 and a overpotential of 670 mV in the presence of trifluoroacetic acid. This electrocatalyst follows a hitherto unobserved HER mechanism involving C-H activation, which manifests as an inverse kinetic isotope effect for the overall hydrogen evolution reaction, and NiI/NiIII intermediates, which have been characterized by EPR spectroscopy. We further validate the possibility of the involvement of NiIII intermediates by the independent synthesis and characterization of organometallic NiIII complexes.

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“…The appearance of the additional catalytic wave could be a result of the homoconjugation process, as expected for a strong acid (p K a TFA in MeCN =12.7) in MeCN [23] . A recent HER study reported for electrocatalytic HER using TFA also showed such additional catalytic redox wave [24] …”

Section: Resultsmentioning

confidence: 63%

“…[23] A recent HER study reported for electrocatalytic HER using TFA also showed such additional catalytic redox wave. [24] Furthermore, the catalytic peak currents increased linearly with the square root of TFA concentrations (Figure 2B) but did not reach an acid-independent regime. Such electrocatalytic behavior can be anticipated because of the background acid-only reduction overlapping within the potential window at < À 1.5 V vs. Fc/Fc + .…”

Section: Resultsmentioning

confidence: 94%

A PEGylated Tin Porphyrin Complex for Electrocatalytic Proton Reduction: Mechanistic Insights into Main‐Group‐Element Catalysis

Chaturvedi

¹

,

McCarver

²

,

Sinha

³

et al. 2022

Angewandte Chemie

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Electrocatalytic proton reduction to form dihydrogen (H 2 ) is an effective way to store energy in the form of chemical bonds. In this study, we validate the applicability of a main-group-element-based tin porphyrin complex as an effective molecular electrocatalyst for proton reduction. A PEGylated Sn porphyrin complex (SnPEGP) displayed high activity (À 4.6 mA cm À 2 at À 1.7 V vs. Fc/Fc + ) and high selectivity (H 2 Faradaic efficiency of 94 % at À 1.7 V vs. Fc/Fc + ) in acetonitrile (MeCN) with trifluoroacetic acid (TFA) as the proton source. The maximum turnover frequency (TOF max ) for H 2 production was obtained as 1099 s À 1 . Spectroelectrochemical analysis, in conjunction with quantum chemical calculations, suggest that proton reduction occurs via an electron-chemical-electron-chemical (ECEC) pathway. This study reveals that the tin porphyrin catalyst serves as a novel platform for investigating molecular electrocatalytic reactions and provides new mechanistic insights into proton reduction.

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“…[23] A recent HER study reported for electrocatalytic HER using TFA also showed such additional catalytic redox wave. [24] Furthermore, the catalytic peak currents increased linearly with the square root of TFA concentrations (Figure 2B) but did not reach an acid-independent regime. Such electrocatalytic behavior can be anticipated because of the background acid-only reduction overlapping within the…”

Section: Methodsmentioning

confidence: 94%

A PEGylated Tin Porphyrin Complex for Electrocatalytic Proton Reduction: Mechanistic Insights into Main‐Group‐Element Catalysis

Chaturvedi

¹

,

McCarver

²

,

Sinha

³

et al. 2022

Self Cite

View full text Add to dashboard Cite

Electrocatalytic proton reduction to form dihydrogen (H 2 ) is an effective way to store energy in the form of chemical bonds. In this study, we validate the applicability of a main-group-element-based tin porphyrin complex as an effective molecular electrocatalyst for proton reduction. A PEGylated Sn porphyrin complex (SnPEGP) displayed high activity (À 4.6 mA cm À 2 at À 1.7 V vs. Fc/Fc + ) and high selectivity (H 2 Faradaic efficiency of 94 % at À 1.7 V vs. Fc/Fc + ) in acetonitrile (MeCN) with trifluoroacetic acid (TFA) as the proton source. The maximum turnover frequency (TOF max ) for H 2 production was obtained as 1099 s À 1 . Spectroelectrochemical analysis, in conjunction with quantum chemical calculations, suggest that proton reduction occurs via an electron-chemical-electron-chemical (ECEC) pathway. This study reveals that the tin porphyrin catalyst serves as a novel platform for investigating molecular electrocatalytic reactions and provides new mechanistic insights into proton reduction.

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Electrocatalytic H₂ evolution promoted by a bioinspired (N2S2)Ni(ii) complex

Abstract: We have investigated a bioinspired (N2S2)Ni(II) electrocatalyst that produces H2 from CF3CO2H with a turnover frequency (TOF) of ~1,250 s–1 at low acid concentration (<0.043 M) in MeCN. A mechanism...

Cited by 13 publications

References 27 publications

Characterization of paramagnetic states in an organometallic nickel hydrogen evolution electrocatalyst

Characterization of paramagnetic states in an organometallic nickel hydrogen evolution electrocatalyst

A PEGylated Tin Porphyrin Complex for Electrocatalytic Proton Reduction: Mechanistic Insights into Main‐Group‐Element Catalysis

A PEGylated Tin Porphyrin Complex for Electrocatalytic Proton Reduction: Mechanistic Insights into Main‐Group‐Element Catalysis

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Electrocatalytic H2 evolution promoted by a bioinspired (N2S2)Ni(ii) complex

Abstract: We have investigated a bioinspired (N2S2)Ni(II) electrocatalyst that produces H2 from CF3CO2H with a turnover frequency (TOF) of ~1,250 s–1 at low acid concentration (<0.043 M) in MeCN. A mechanism...

Cited by 13 publications

References 27 publications

Characterization of paramagnetic states in an organometallic nickel hydrogen evolution electrocatalyst

Characterization of paramagnetic states in an organometallic nickel hydrogen evolution electrocatalyst

A PEGylated Tin Porphyrin Complex for Electrocatalytic Proton Reduction: Mechanistic Insights into Main‐Group‐Element Catalysis

A PEGylated Tin Porphyrin Complex for Electrocatalytic Proton Reduction: Mechanistic Insights into Main‐Group‐Element Catalysis

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Electrocatalytic H₂ evolution promoted by a bioinspired (N2S2)Ni(ii) complex