Imaging and Quantifying the Formation of Single Nanobubbles at Single Platinum Nanoparticles during the Hydrogen Evolution Reaction

Abstract

While numerous efforts are produced towards the design of sustainable and efficient nano-catalysts of hydrogen evolution reaction (HER), there is a need for the operando observation and quantification of gas nanobubbles (NBs) formation involved in this electrochemical reaction. It is achieved herein through interference reflection microscopy (IRM) coupled to electrochemistry and optical modelling. Besides analyzing the geometry and growth rate of individual NBs at single nanocatalysts, the toolbox offered by super-localization and quantitative label-free optical microscopy allows analyzing the geometry (contact angle and footprint with surface) of individual NBs and their growth rate. It turns out that after few seconds, NBs are steadily growing while they are fully covering the Pt NPs that allowed their nucleation and their pinning on the electrode surface. It then raises relevant questions related to gas evolution catalysts as for example: does the evaluation of NB growth at single nano-catalyst really reflect its electrochemical activity? 2

Deciphering Competitive Routes for Nickel‐Based Nanoparticle Electrodeposition by an Operando Optical Monitoring

“…The sudden drop in nucleation events highlights the increased predominance of water reduction at potentials below −1.5 V. Moreover, the final NP size decreases as its onset potential becomes more negative: the earlier a NP nucleates, the larger it is at the end of the LSV, as time and reduction goes on. This situation is generally encountered in progressive electrochemical nucleation processes, for example, NPs electrodeposition [20] or gas nanobubbles generation [27] . If it is also detected during the self‐limited Ni growth, it is likely because the pH increases homogeneously over the NPs ensemble.…”

“…coupling electrochemistry to high resolution label-free optical microscopy [15][16][17] has proved to be effective to monitor metal deposition at single NPs with high temporal resolution and sensitivity, [18][19][20][21] as well as to differentiate metallic NPs from other nanoobjects (e.g. dielectric NPs, [22][23][24][25] gas nanobubbles [26,27] ).…”

“…This situation is generally encountered in progressive electrochemical nucleation processes, for example, NPs electrodeposition [20] or gas nanobubbles generation. [27] If it is also detected during the self-limited Ni growth, it is likely because the pH increases homogeneously over the NPs ensemble. Overall, water reduction limits Ni 2+ reduction not only by limiting the growth of already nucleated Ni NPs, but also by limiting the formation of new nuclei.…”

Deciphering Competitive Routes for Nickel‐Based Nanoparticle Electrodeposition by an Operando Optical Monitoring

“…coupling electrochemistry to high resolution label‐free optical microscopy [15–17] has proved to be effective to monitor metal deposition at single NPs with high temporal resolution and sensitivity, [18–21] as well as to differentiate metallic NPs from other nanoobjects (e.g. dielectric NPs, [22–25] gas nanobubbles [26, 27] ).…”

Unravelling the last milliseconds of an individual graphene nanoplatelet before impact with a Pt surface by bipolar electrochemistry

“…Single entity electrochemistry proved to be a powerful method to study individual nanoparticles. [7][8][9][10][11][12] The high temporal resolution of electrochemical measurements allows probing dynamics of electro-catalysis, [13][14][15][16][17] electrolysis, [18][19][20][21][22][23] electro-nucleation and growth, [24][25][26][27][28][29][30] as well as motion of individual particles. [31][32][33][34][35] For example, several groups showed that Ag nanoparticles (Ag NP) may rebound several times on the surface of the electrode before being completely oxidized.…”