Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Cooperative electrocatalytic alcohol oxidation with electron-proton-transfer mediators


The electrochemical oxidation of alcohols is a major focus of energy and chemical conversion efforts, with potential applications ranging from fuel cells to biomass utilization and fine-chemical synthesis1,2,3,4,5,6,7. Small-molecule electrocatalysts for processes of this type are promising targets for further development8, as demonstrated by recent advances in nickel catalysts for electrochemical production and oxidation of hydrogen9,10,11. Complexes with tethered amines that resemble the active site of hydrogenases12 have been shown both to catalyse hydrogen production (from protons and electrons) with rates far exceeding those of such enzymes11,13 and to mediate reversible electrocatalytic hydrogen production and oxidation with enzyme-like performance14. Progress in electrocatalytic alcohol oxidation has been more modest. Nickel complexes similar to those used for hydrogen oxidation have been shown to mediate efficient electrochemical oxidation of benzyl alcohol, with a turnover frequency of 2.1 per second. These compounds exhibit poor reactivity with ethanol and methanol, however15. Organic nitroxyls, such as TEMPO (2,2,6,6-tetramethyl-1-piperidine N-oxyl), are the most widely studied electrocatalysts for alcohol oxidation5,6,7,16,17,18,19. These catalysts exhibit good activity (1–2 turnovers per second) with a wide range of alcohols18 and have great promise for electro-organic synthesis7. Their use in energy-conversion applications, however, is limited by the high electrode potentials required to generate the reactive oxoammonium species. Here we report (2,2′-bipyridine)Cu/nitroxyl co-catalyst systems for electrochemical alcohol oxidation that proceed with much faster rates, while operating at an electrode potential a half-volt lower than that used for the TEMPO-only process. The (2,2′-bipyridine)Cu(II) and TEMPO redox partners exhibit cooperative reactivity and exploit the low-potential, proton-coupled TEMPO/TEMPOH redox process rather than the high-potential TEMPO/TEMPO+ process. The results show how electron-proton-transfer mediators, such as TEMPO, may be used in combination with first-row transition metals, such as copper, to achieve efficient two-electron electrochemical processes, thereby introducing a new concept for the development of non-precious-metal electrocatalysts.

This is a preview of subscription content

Access options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.

Figure 1: Molecular electrocatalysts and related homogeneous and enzymatic catalysts.
Figure 2: Cyclic voltammogram of a solution of (bpy)Cu(OTf) and TEMPO and spectrophotometric evidence for (bpy)Cu(II)-mediated oxidation of TEMPOH (and benzyl alcohol) under anaerobic conditions.
Figure 3: Electrochemical oxidation of benzyl alcohol with (bpy)Cu/TEMPO and TEMPO catalysts.
Figure 4: Electronic effects and comparative reactivity of different catalyst systems with different alcohols.


  1. 1

    Kakati, N. et al. Anode catalysts for direct methanol fuel cells in acidic media: do we have any alternative for Pt or Pt−Ru? Chem. Rev. 114, 12397–12429 (2014)

    CAS  Article  Google Scholar 

  2. 2

    Bianchini, C. & Shen, P. K. Palladium-based electrocatalysts for alcohol oxidation in half cells and in direct alcohol fuel cells. Chem. Rev. 109, 4183–4206 (2009)

    CAS  Article  Google Scholar 

  3. 3

    Cheung, K.-C., Wong, W.-L., Ma, D.-L., Lai, T.-S. & Wong, K.-Y. Transition metal complexes as electrocatalysts—development and applications in electro-oxidation reactions. Coord. Chem. Rev. 251, 2367–2385 (2007)

    CAS  Article  Google Scholar 

  4. 4

    Trincado, M., Banerjee, D. & Grützmacher, H. Molecular catalysts for hydrogen production from alcohols. Energy Environ. Sci. 7, 2464–2503 (2014)

    CAS  Article  Google Scholar 

  5. 5

    Hickey, D. P., McCammant, M. S., Giroud, F., Sigman, M. S. & Minteer, S. D. Hybrid enzymatic and organic electrocatalytic cascade for the complete oxidation of glycerol. J. Am. Chem. Soc. 136, 15917–15920 (2014)

    CAS  Article  Google Scholar 

  6. 6

    Cha, H. G. & Choi, K.-S. Combined biomass valorization and hydrogen production in a photoelectrochemical cell. Nat. Chem. 7, 328–333 (2015)

    CAS  Article  Google Scholar 

  7. 7

    Ciriminna, R., Palmisano, G. & Pagliaro, M. Electrodes functionalized with the 2,2,6,6-tetramethylpiperidinyloxy radical for the waste-free oxidation of alcohols. ChemCatChem 7, 552–558 (2015)

    CAS  Article  Google Scholar 

  8. 8

    Francke, R. & Little, R. D. Redox catalysis in organic electrosynthesis: basic principles and recent developments. Chem. Soc. Rev. 43, 2492–2521 (2014)

    CAS  Article  Google Scholar 

  9. 9

    Rakowski Dubois, M. & Dubois, D. L. Development of molecular electrocatalysts for CO2 reduction and H2 production/oxidation. Acc. Chem. Res. 42, 1974–1982 (2009)

    CAS  Article  Google Scholar 

  10. 10

    Le Goff, A. et al. From hydrogenases to noble metal-free catalytic nanomaterials for H2 production and uptake. Science 326, 1384–1387 (2009)

    ADS  CAS  Article  Google Scholar 

  11. 11

    Raugei, S. et al. Experimental and computational mechanistic studies guiding the rational design of molecular electrocatalysts for production and oxidation of hydrogen. Inorg. Chem. 55, 445–460 (2016)

    CAS  Article  Google Scholar 

  12. 12

    Rauchfuss, T. B. Diiron azadithiolates as models for the [FeFe]-hydrogenase active site and paradigm for the role of the second coordination sphere. Acc. Chem. Res. 48, 2107–2116 (2015)

    CAS  Article  Google Scholar 

  13. 13

    Helm, M. L., Stewart, M. P., Bullock, R. M., Rakowski DuBois, M. & DuBois, D. L. A synthetic nickel electrocatalyst with a turnover frequency above 100,000 s−1 for H2 production. Science 333, 863–866 (2011)

    ADS  CAS  Article  Google Scholar 

  14. 14

    Rodriguez-Maciá, P., Dutta, A., Lubitz, W., Shaw, W. J. & Rüdiger, O. Direct comparison of the performance of a bio-inspired synthetic nickel catalyst and a [NiFe]-hydrogenase, both covalently attached to electrodes. Angew. Chem. Int. Ed. 54, 12303–12307 (2015)

    Article  Google Scholar 

  15. 15

    Weiss, C. J., Wiedner, E. S., Roberts, J. A. S. & Appel, A. M. Nickel phosphine catalysts with pendant amines for electrocatalytic oxidation of alcohols. Chem. Commun. 51, 6172–6174 (2015)

    CAS  Article  Google Scholar 

  16. 16

    Bobbitt, J. M., Brückner, C. & Merbouh, N. Oxoammonium- and nitroxide-catalyzed oxidations of alcohols. Org. React. 74, 103–424 (2009)

    CAS  Google Scholar 

  17. 17

    Semmelhack, M. F., Chou, C. S. & Cortes, D. A. Nitroxyl-mediated electrooxidation of alcohols to aldehydes and ketones. J. Am. Chem. Soc. 105, 4492–4494 (1983)

    CAS  Article  Google Scholar 

  18. 18

    Rafiee, M., Miles, K. C. & Stahl, S. S. Electrocatalytic alcohol oxidation with TEMPO and bicyclic nitroxyl derivatives: driving force trumps steric effects. J. Am. Chem. Soc. 137, 14751–14757 (2015)

    CAS  Article  Google Scholar 

  19. 19

    Hickey, D. P. et al. Predicting electrocatalytic properties: modeling structure-activity relationships of nitroxyl radicals. J. Am. Chem. Soc. 137, 16179–16186 (2015)

    CAS  Article  Google Scholar 

  20. 20

    Ryland, B. L. & Stahl, S. S. Practical aerobic oxidations of alcohols and amines with homogeneous copper/TEMPO and related catalyst systems. Angew. Chem. Int. Ed. 53, 8824–8838 (2014)

    CAS  Article  Google Scholar 

  21. 21

    Semmelhack, M. F., Schmid, C. R., Cortes, D. A. & Chou, C. S. Oxidation of alcohols to aldehydes with oxygen and cupric ion, mediated by nitrosonium ion. J. Am. Chem. Soc. 106, 3374–3376 (1984)

    CAS  Article  Google Scholar 

  22. 22

    Dijksman, A., Arends, I. W. C. E. & Sheldon, R. A. Cu(II)-nitroxyl radicals as catalytic galactose oxidase mimics. Org. Biomol. Chem. 1, 3232–3237 (2003)

    CAS  Article  Google Scholar 

  23. 23

    Hoover, J. M., Ryland, B. L. & Stahl, S. S. Mechanism of copper(I)/TEMPO-catalyzed aerobic alcohol oxidation. J. Am. Chem. Soc. 135, 2357–2367 (2013)

    CAS  Article  Google Scholar 

  24. 24

    Ryland, B. L., McCann, S. D., Brunold, T. C. & Stahl, S. S. Mechanism of alcohol oxidation mediated by copper(II) and nitroxyl radicals. J. Am. Chem. Soc. 136, 12166–12173 (2014)

    CAS  Article  Google Scholar 

  25. 25

    Whittaker, J. W. Free radical catalysis by galactose oxidase. Chem. Rev. 103, 2347–2364 (2003)

    CAS  Article  Google Scholar 

  26. 26

    Chirik, P. J. & Wieghardt, K. Radical ligands confer nobility on base-metal catalysts. Science 327, 794–795 (2010)

    ADS  CAS  Article  Google Scholar 

  27. 27

    Costentin, C. & Savéant, J.-M. Multielectron, multistep molecular catalysis of electrochemical reactions: benchmarking of homogeneous catalysts. ChemElectroChem 1, 1226–1236 (2014)

    CAS  Article  Google Scholar 

  28. 28

    Semmelhack, M. F., Schmid, C. R. & Cortes, D. A. Mechanism of the oxidation of alcohols by 2,2,6,6-tetramethylpiperidine nitrosonium cation. Tetrahedr. Lett. 27, 1119–1122 (1986)

    CAS  Article  Google Scholar 

  29. 29

    Huynh, M. H. V. & Meyer, T. J. Proton-coupled electron transfer. Chem. Rev. 107, 5004–5064 (2007)

    CAS  Article  Google Scholar 

  30. 30

    Warren, J. J., Tronic, T. A. & Mayer, J. M. Thermochemistry of proton-coupled electron transfer reagents and its implications. Chem. Rev. 110, 6961–7001 (2010)

    CAS  Article  Google Scholar 

Download references


Financial support for this project was provided by the Great Lakes Bioenergy Research Center (Department of Energy Biological and Environmental Research Office of Science DE-FC02-07ER64494).

Author information




S.S.S. conceived the idea for the Cu/nitroxyl electrocatalytic alcohol oxidation, and A.B. and S.S.S. collaborated to design the project. A.B. performed all experimental work and led the data interpretation and analysis, in consultation with S.S.S. A.B. and S.S.S. wrote the manuscript.

Corresponding author

Correspondence to Shannon S. Stahl.

Ethics declarations

Competing interests

The authors declare no competing financial interests.

Supplementary information

Supplementary Information

This file contains Supplementary Text and Data, Supplementary Figures 1 – 23 and additional references (see Contents for more details). (PDF 10424 kb)

PowerPoint slides

Rights and permissions

Reprints and Permissions

About this article

Verify currency and authenticity via CrossMark

Cite this article

Badalyan, A., Stahl, S. Cooperative electrocatalytic alcohol oxidation with electron-proton-transfer mediators. Nature 535, 406–410 (2016).

Download citation

Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing