Heterogeneous electrochemical phenomena, such as (photo)electrochemical water splitting to generate hydrogen using semiconductors and/or electrocatalysts, are driven by the accumulated charge carriers and thus the interfacial electrochemical potential gradients that promote charge transfer. However, measurements of the “surface” electrochemical potential during operation are not generally possible using conventional electrochemical techniques, which measure/control the potential of a conducting electrode substrate. Here we show that the nanoscale conducting tip of an atomic force microscope cantilever can sense the surface electrochemical potential of electrocatalysts in operando. To demonstrate utility, we measure the potential-dependent and thickness-dependent electronic properties of cobalt (oxy)hydroxide phosphate (CoPi). We then show that CoPi, when deposited on illuminated haematite (α-Fe2O3) photoelectrodes, acts as both a hole collector and an oxygen evolution catalyst. We demonstrate the versatility of the technique by comparing surface potentials of CoPi-decorated planar and mesoporous haematite and discuss viability for broader application in the study of electrochemical phenomena.
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Walter, M. G. et al. Solar water splitting cells. Chem. Rev. 110, 6446–6473 (2010).
Sivula, K. & Van de Krol, R. Semiconducting materials for photoelectrochemical energy conversion. Nat. Rev. Mater. 1, 15015 (2016).
Zandi, O. & Hamann, T. W. The potential versus current state of water splitting with hematite. Phys. Chem. Chem. Phys. 17, 22485–22503 (2015).
Sivula, K. Metal oxide photoelectrodes for solar fuel production, surface traps, and catalysis. J. Phys. Chem. Lett. 4, 1624–1633 (2013).
Cowan, A. J. & Durrant, J. R. Long-lived charge separated states in nanostructured semiconductor photoelectrodes for the production of solar fuels. Chem. Soc. Rev. 42, 2281–2293 (2013).
Montoya, J. H. et al. Materials for solar fuels and chemicals. Nat. Mater. 16, 70–81 (2017).
Barroso, M. et al. Dynamics of photogenerated holes in surface modified α-Fe2O3 photoanodes for solar water splitting. Proc. Natl Acad. Sci. USA 109, 15640–15645 (2012).
Barroso, M. et al. The role of cobalt phosphate in enhancing the photocatalytic activity of α-Fe2O3 toward water oxidation. J. Am. Chem. Soc. 133, 14868–14871 (2011).
Klahr, B. M., Gimenez, S., Fabregat-Santiago, F., Bisquert, J. & Hamann, T. W. Photoelectrochemical and impedance spectroscopic investigation of water oxidation with ‘Co–Pi’-coated hematite electrodes. J. Am. Chem. Soc. 134, 16693–16700 (2012).
Carroll, G. M., Zhong, D. K. & Gamelin, D. R. Mechanistic insights into solar water oxidation by cobalt-phosphate-modified α-Fe2O3 photoanodes. Energy Environ. Sci. 8, 577–584 (2015).
Carroll, G. M. & Gamelin, D. R. Kinetic analysis of photoelectrochemical water oxidation by mesostructured Co-Pi/α-Fe2O3 photoanodes. J. Mater. Chem. A 4, 2986–2994 (2016).
Lin, F. & Boettcher, S. W. Adaptive semiconductor/electrocatalyst junctions in water-splitting photoanodes. Nat. Mater. 13, 81–86 (2014).
Nellist, M. R., Laskowski, F. A. L., Lin, F., Mills, T. J. & Boettcher, S. W. Semiconductor–electrocatalyst interfaces: theory, experiment, and applications in photoelectrochemical water splitting. Acc. Chem. Res. 49, 733–740 (2016).
Lin, F., Bachman, B. F. & Boettcher, S. W. Impact of electrocatalyst activity and ion permeability on water-splitting photoanodes. J. Phys. Chem. Lett. 6, 2427–2433 (2015).
Mills, T. J., Lin, F. & Boettcher, S. W. Theory and simulations of electrocatalyst-coated semiconductor electrodes for solar water splitting. Phys. Rev. Lett. 112, 148304 (2014).
Laskowski, F. A. L., Nellist, M. R., Venkatkarthick, R. & Boettcher, S. W. Junction behavior of n-Si photoanodes protected by thin Ni elucidated from dual working electrode photoelectrochemistry. Energy Environ. Sci. 10, 570–579 (2017).
Qiu, J. et al. Direct in situ measurement of charge transfer processes during photoelectrochemical water oxidation on catalyzed hematite. ACS Cent. Sci. 3, 1015–1025 (2017).
Hurth, C., Li, C. & Bard, A. J. Direct probing of electrical double layers by scanning electrochemical potential microscopy. J. Phys. Chem. C 111, 4620–4627 (2007).
Yoon, Y. et al. A nanometer potential probe for the measurement of electrochemical potential of solution. Electrochim. Acta 52, 4614–4621 (2007).
Yoon, Y., Woo, D., Shin, T., Chung, T. D. & Kang, H. Real-space investigation of electrical double layers. Potential gradient measurement with a nanometer potential probe. J. Phys. Chem. C 115, 17384–17391 (2011).
Woo, D., Yoo, J., Park, S., Jeon, I. C. & Kang, H. Direct probing into the electrochemical interface using a novel potential probe: Au(111) electrode/NaBF4 solution interface. Bull. Korean Chem. Soc. 25, 577–580 (2004).
Baier, C. & Stimming, U. Imaging single enzyme molecules under in situ conditions. Angew. Chemie Int. Ed. 48, 5542–5544 (2009).
Hamou, R. F., Biedermann, P. U., Erbe, A. & Rohwerder, M. Numerical analysis of Debye screening effect in electrode surface potential mapping by scanning electrochemical potential microscopy. Electrochem. Commun. 12, 1391–1394 (2010).
Traunsteiner, C., Tu, K. & Kunze-Liebhauser, J. High-resolution imaging of the initial stages of oxidation of Cu(111) with scanning electrochemical potential microscopy. ChemElectroChem 2, 77–84 (2015).
Domanski, A. L. et al. Kelvin probe force microscopy in nonpolar liquids. Langmuir 28, 13892–13899 (2012).
Collins, L. et al. Probing charge screening dynamics and electrochemical processes at the solid–liquid interface with electrochemical force microscopy. Nat. Commun. 5, 3871 (2014).
Collins, L. et al. Kelvin probe force microscopy in liquid using electrochemical force microscopy. Beilstein J. Nanotechnol. 6, 201–214 (2015).
Kobayashi, N., Asakawa, H. & Fukuma, T. Nanoscale potential measurements in liquid by frequency modulation atomic force microscopy. Rev. Sci. Instrum. 81, 123705 (2010).
Kobayashi, N., Asakawa, H. & Fukuma, T. Dual frequency open-loop electric potential microscopy for local potential measurements in electrolyte solution with high ionic strength. Rev. Sci. Instrum. 83, 33709 (2012).
Kanan, M. W. & Nocera, D. G. In situ formation of an oxygen-evolving catalyst in neutral water containing phosphate and Co2+. Science 321, 1072–1075 (2008).
Lutterman, D. A., Surendranath, Y. & Nocera, D. G. A self-healing oxygen-evolving catalyst. J. Am. Chem. Soc. 131, 3838–3839 (2009).
Huang, Z. et al. PeakForce scanning electrochemical microscopy with nanoelectrode probes. Microsc. Today 24, 18–25 (2016).
Nellist, M. R. et al. Atomic force microscopy with nanoelectrode tips for high resolution electrochemical, nanoadhesion and nanoelectrical imaging. Nanotechnology 28, 95711 (2017).
Costentin, C., Porter, T. R. & Savéant, J.-M. Conduction and reactivity in heterogeneous-molecular catalysis: new insights in water oxidation catalysis by phosphate cobalt oxide films. J. Am. Chem. Soc. 138, 5615–5622 (2016).
Andrieux, C. P., Costentin, C., Di Giovanni, C., Savéant, J.-M. & Tard, C. Conductive mesoporous catalytic films. Current distortion and performance degradation by dual-phase ohmic drop effects. Analysis and remedies. J. Phys. Chem. C 120, 21263–21271 (2016).
Burke, M. S., Kast, M. G., Trotochaud, L., Smith, A. M. & Boettcher, S. W. Cobalt–iron (oxy)hydroxide oxygen evolution electrocatalysts: the role of structure and composition on activity, stability, and mechanism. J. Am. Chem. Soc. 137, 3638–3648 (2015).
Burke, M. S. et al. Revised oxygen evolution reaction activity trends for first-row transition-metal (oxy)hydroxides in alkaline media. J. Phys. Chem. Lett. 6, 3737–3742 (2015).
Klingan, K. et al. Water oxidation by amorphous cobalt-based oxides: volume activity and proton transfer to electrolyte bases. ChemSusChem 7, 1301–1310 (2014).
Jörissen, L. Bifunctional oxygen/air electrodes. J. Power Sources 155, 23–32 (2006).
Doyle, R. L. & Lyons, M. E. G. An electrochemical impedance study of the oxygen evolution reaction at hydrous iron oxide in base. Phys. Chem. Chem. Phys. 15, 5224–5237 (2013).
Batchellor, A. S. & Boettcher, S. W. Pulse-electrodeposited Ni–Fe (oxy)hydroxide oxygen evolution electrocatalysts with high geometric and intrinsic activities at large mass loadings. ACS Catal. 5, 6680–6689 (2015).
Klahr, B. M., Martinson, A. B. F. & Hamann, T. W. Photoelectrochemical investigation of ultrathin film iron oxide solar cells prepared by atomic layer deposition. Langmuir 27, 461–468 (2011).
Tilley, S. D., Cornuz, M., Sivula, K. & Grätzel, M. Light-induced water splitting with hematite: improved nanostructure and iridium oxide catalysis. Angew. Chemie Int. Ed. 49, 6405–6408 (2010).
Kay, A., Cesar, I. & Grätzel, M. New benchmark for water photooxidation by nanostructured α-Fe2O3 films. J. Am. Chem. Soc. 128, 15714–15721 (2006).
Ma, Y., Kafizas, A., Pendlebury, S. R., Le Formal, F. & Durrant, J. R. Photoinduced absorption spectroscopy of CoPi on BiVO4: the function of CoPi during water oxidation. Adv. Funct. Mater. 26, 4951–4960 (2016).
Ma, Y., Le Formal, F., Kafizas, A., Pendlebury, S. R. & Durrant, J. R. Efficient suppression of back electron/hole recombination in cobalt phosphate surface-modified undoped bismuth vanadate photoanodes. J. Mater. Chem. A 3, 20649–20657 (2015).
Kennedy, J. H. & Frese, K. W. Photooxidation of water at α-Fe2O3 electrodes. J. Electrochem. Soc. 125, 709–714 (1978).
Zandi, O., Schon, A. R., Hajibabaei, H. & Hamann, T. W. Enhanced charge separation and collection in high-performance electrodeposited hematite films. Chem. Mater. 28, 765–771 (2016).
Honbo, K. et al. Visualizing nanoscale distribution of corrosion cells by open-loop electric potential microscopy. ACS Nano 10, 2575–2583 (2016).
Klahr, B. M., Gimenez, S., Fabregat-Santiago, F., Hamann, T. W. & Bisquert, J. Water oxidation at hematite photoelectrodes: the role of surface states. J. Am. Chem. Soc. 134, 4294–4302 (2012).
Zandi, O. & Hamann, T. W. Enhanced water splitting efficiency through selective surface state removal. J. Phys. Chem. Lett. 5, 1522–1526 (2014).
Dezelah, C. L., Niinistö, J., Arstila, K., Niinistö, L. & Winter, C. H. Atomic layer deposition of Ga2O3 films from a dialkylamido-based precursor. Chem. Mater. 18, 471–475 (2006).
Surendranath, Y., Kanan, M. W. & Nocera, D. G. Mechanistic studies of the oxygen evolution reaction by a cobalt-phosphate catalyst at neutral pH. J. Am. Chem. Soc. 132, 16501–16509 (2010).
Risch, M. et al. Cobalt–oxo core of a water-oxidizing catalyst film. J. Am. Chem. Soc. 131, 6936–6937 (2009).
Kanan, M. W. et al. Structure and valency of a cobalt-phosphate water oxidation catalyst determined by in situ X-ray spectroscopy. J. Am. Chem. Soc. 132, 13692–13701 (2010).
Surendranath, Y., Dinca, M. & Nocera, D. G. Electrolyte-dependent electrosynthesis and activity of cobalt-based water oxidation catalysts. J. Am. Chem. Soc. 131, 2615–2620 (2009).
This work was supported by the Department of Energy, Basic Energy Sciences, Award DE-SC0014279. S.W.B also thanks the Sloan and Dreyfus Foundations for additional support. The atomic force microscope was purchased using funds provided by the NSF Major Research Instrumentation Program, Grant DMR-1532225. The growth of the planar haematite electrodes was supported by NSF Award CHE-1664823. F.A.L.L. acknowledges funding from the NSF GRFP, Grant 1309047. We thank Dr Fuding Lin, Dr Michaela B. Stevens, Dr Matthew G. Kast, Dr Sebastian Oener and Lisa J. Enman for helpful conversations, Dr Christian Dette for assistance in preparing figures, Dr Zhuangqun Huang for technical assistance with the AFM and John Boosinger for help designing the electrochemistry cell.
The authors declare no competing financial interests.
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Nellist, M.R., Laskowski, F.A.L., Qiu, J. et al. Potential-sensing electrochemical atomic force microscopy for in operando analysis of water-splitting catalysts and interfaces. Nat Energy 3, 46–52 (2018). https://doi.org/10.1038/s41560-017-0048-1
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