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@INPROCEEDINGS{Schatz:911423,
      author       = {Schatz, Michael and Jovanovic, Sven and Eichel, Rüdiger-A.
                      and Granwehr, Josef},
      title        = {{M}easuring local p{H} gradients using $^{13}{C}$ magnetic
                      resonance imaging},
      reportid     = {FZJ-2022-04706},
      year         = {2022},
      abstract     = {In the light of the ever-increasing number of new catalyst
                      materials for the CO2 reduction reaction (CO2RR),
                      determination of local conditions in electrode proximity is
                      crucial to understand and improve the performance of
                      electrolysis. Especially the widespread use of KHCO3 in low
                      concentrations clearly demonstrates the importance of the
                      choice of electrolyte for the catalysis of this reaction,
                      since its low buffer capacity leads to increased pH in
                      proximity to the electrode. This promotes C2+ product
                      reaction pathways, while simultaneously suppressing
                      unfavourable CH4 and H2 formation. Measuring local pH values
                      on CO2RR-catalyst surfaces has been attempted by optical
                      methods and by scanning probe microscopy. In our recent
                      work, we presented a NMR method for determining local pH in
                      KHCO3 electrolyte at a Cu electrode using the 13C resonances
                      of the CO2/HCO3-/CO32- equilibrium. The present study adds a
                      spatial dimension to this technique in order to investigate
                      evolution of local pH and concentration gradients over time
                      in the electrochemical cell illustrated in Fig. 1a.Spatially
                      resolved 13C spectra of the averaged carbonate (HCO3-/CO32-)
                      resonance are presented in Fig. 1b. The electrode was placed
                      at z = 0 mm. Before electrolysis, the carbonate peak had a
                      constant chemical shift along the z-direction. As a constant
                      potential was applied, the peak locally shifted downfield,
                      which corresponds to a local pH increase. These pH gradients
                      are quantified by fitting Lorentzian functions to the peaks.
                      In Fig. 1c, resulting z-profiles of the chemical shift of
                      the carbonate peak and their development over time are
                      depicted. A sudden increase of near-electrode pH at the
                      beginning of the electrolysis was observed, followed by an
                      assimilation of local and bulk values. In this study, it
                      will be shown that chemical shift imaging is successfully
                      applied in operando to resolve the spatial distribution of
                      pH value and electrolyte concentrations in the vicinity of a
                      Cu electrode during CO2RR. The evolution of these values as
                      a function of time are in accordance with theory.},
      month         = {Sep},
      date          = {2022-09-27},
      organization  = {Electrochemistry 2022 "At the
                       Interface between Chemistry and
                       Physics", Berlin (Germany), 27 Sep 2022
                       - 30 Sep 2022},
      subtyp        = {After Call},
      cin          = {IEK-9},
      cid          = {I:(DE-Juel1)IEK-9-20110218},
      pnm          = {1232 - Power-based Fuels and Chemicals (POF4-123) / DFG
                      project 390919832 - EXC 2186: Das Fuel Science Center –
                      Adaptive Umwandlungssysteme für erneuerbare Energie- und
                      Kohlenstoffquellen (390919832) / HITEC - Helmholtz
                      Interdisciplinary Doctoral Training in Energy and Climate
                      Research (HITEC) (HITEC-20170406)},
      pid          = {G:(DE-HGF)POF4-1232 / G:(GEPRIS)390919832 /
                      G:(DE-Juel1)HITEC-20170406},
      typ          = {PUB:(DE-HGF)6},
      url          = {https://juser.fz-juelich.de/record/911423},
}