page_title: Virtual breakdown mechanism
section_title: Pure water electrolysis in nanogap cell
hierarchical_section_title: Virtual breakdown mechanism / Pure water electrolysis / Pure water electrolysis in nanogap cell
caption_attribution_description: English: In nanogap cell, high electric field in the entire gap can enhance water ionization and mass transport (mainly migration), leading to pure water splitting efficiently limited by electron-transfer.
context_page_description: Virtual breakdown mechanism is a concept in the field of electrochemistry. In electrochemical reactions, when the cathode and the anode are close enough to each other, the double layer regions from the two electrodes can be overlapped, forming large electric field uniformly distributed inside the entire electrode gap. Such high electric field can significantly enhance the ion migration inside bulk solution, and thus facilitate the entire reaction rate, performing like "breakdown" of the reactant. However, it is fundamentally different from the meaning of traditional "breakdown".
  Virtual breakdown mechanism is discovered in 2017 when researchers studied pure water electrolysis based on deep-sub-Debye-length nanogap electrochemical cells. Furthermore, researchers found the size effect of the gap distance between cathodes and anodes to the performance of electrochemical reactions.
context_section_description: In nanogap cells, high electric field can distribute uniformly in the entire gap (see section "Electric field distribution"). Different from ion transport in macrosystem, now newly-generated OH⁻ ions can be immediately migrated from cathode to anode. In the case where the two electrodes are close enough, the mass transport rate can be even larger than the electron-transfer rate, resulting in such OH⁻ ions waiting for electron-transfer at the anode, rather than accumulated at the cathode. In this way, the entire reaction can keep going and no self-stopped.
  Notice that, for pure water electrolysis in nanogap cells, the net OH⁻ ion accumulation near the anode not only increases the local reactant concentration, but also decreases the overpotential requirement (as in the Frumkin effect). According to Butler–Volmer equation, such ions accumulation can increase the electrolysis current, a.k.a., water splitting throughput and efficiency.
  The traditional view should be revised that even pure water can be efficiently electrolyzed, when the electrode gap is small enough.
caption: In nanogap cell, high electric field in the entire gap can enhance water ionization and mass transport (mainly migration), leading to pure water splitting efficiently limited by electron-transfer.
exif: {}