What is limiting the potential window in aqueous sodium‐ion batteries? Online study of the hydrogen‐, oxygen‐ and CO₂‐evolution reactions at NaTi₂(PO₄)₃ and Na_0.44MnO₂ electrodes

Abstract

NaTi2(PO4)3 (NTP) and Na0.44MnO2 (NMO), and their derivatives, have emerged as the most promising materials for aqueous Na‐ion batteries. For both, NTP and NMO, avoiding the evolution of hydrogen and oxygen is found to be mandatory in order to mitigate material dissolution. Intriguingly, however, no direct determination of the hydrogen and oxygen evolution reactions (HER and OER) has yet been carried out. Using differential electrochemical mass spectrometry (DEMS) we directly identify the onset potentials for the HER and OER. Surprisingly, the potential window is found to be significantly smaller than suggested by commonly employed cyclic voltammetry measurements. CO2 evolution, upon decomposition of carbon black, is observed at an onset potential of 1.61 VRHE, which is 0.25 V more cathodic than the OER for the NMO electrode. Our results show that the state‐of‐the‐art carbon additive plays a crucial role in the stability of the positive NMO electrode in the ion battery.

The Relevance of the Interfacial Water Reactivity for Electrochemical CO Reduction on Copper Single Crystals

“…For all experiments, a PEEK flow cell (Hiden Analytical, U.K.) with a constant electrolyte flow rate of 50 μL min –1 was used. Further information on the setup and the delay time can be found elsewhere. − A Metrohm Autolab (PGSTAT 302N) was used as potentiostat. The scan rate was 2 mV s –1 , and the m / z signals of 2 (hydrogen, H 2 + ), 15 (methane, CH 3 + ) and 26 (ethylene, C 2 H 2 + ) were simultaneously recorded.…”

Enhanced Electrochemical Performance of NTP/C with Rutile TiO2 Coating, as Anode Material for Sodium‐Ion Batteries

“…[11,13] For aqueous rechargeable SIBs, even though a lot of research has been devoted into this field, there are still major challenges that have to be overcome before its successful commercialization. [15] Among many anode and cathode materials, which have been tested in aqueous systems, especially carbon-coated NaTi 2 (PO 4 ) 3 has been proven to show great battery performance characteristics. NTP is considered as promising insertion-type anode material for aqueous, as well as for non-aqueous SIBs.…”

“…For aqueous rechargeable SIBs, even though a lot of research has been devoted into this field, there are still major challenges that have to be overcome before its successful commercialization [15] …”