In-situ monitoring of hydrogen peroxide production at nickel single-atom electrocatalyst.

[Display omitted] • An electro-production and detection of H 2 O 2 system is constructed by Ni-SAC. • In-situ electro-detection of H 2 O 2 is more reliable than spectrophotometry. • The sensor displays a low detection limit of 6.87 pM towards H 2 O 2 detection. • NiOOH on single Ni site is an intermediate for H 2 O 2 detection in alkaline medium. Electrochemical oxygen reduction reaction (ORR) to hydrogen peroxide (H 2 O 2) is a common method to address the growing demands of H 2 O 2. To map a clear understanding of structure–activity relationship of electrocatalyst for H 2 O 2 production, it is necessary to real-time quantitative monitor of H 2 O 2 in the initial production process. However, we found that the common off-line methods such as spectrophotometry, titration, etc., are not reliably during in-situ ORR process. Here, a simple and real-time simultaneous electrochemical production and determination of H 2 O 2 system is constructed by using a dual-functional nickel (Ni) single-atom electrocatalyst. The electro-production part is conducted with a DC power supply, air pump, and dual-electrode system, while the electro-detection part consists of a three-electrode system. Compared with traditional off-line H 2 O 2 measure methods, the present on-line determination of H 2 O 2 protocol provides more reliable results in the quantitative monitoring of H 2 O 2 , and with a wide detection concentration range from 20 pM to 22.2 mM and a low detection limit of 6.87 pM. NiOOH on single Ni site is an important intermediate for efficient detection of H 2 O 2 in alkaline medium. The Ni-SAC sensor also shows well anti-interferential and selective ability, high reproducibility and stability of H 2 O 2 sensing up to 12 days. This simple-to-operate method offers a new window to record a reliable structure–activity relationship on electrocatalyst engineering in electrochemistry. [ABSTRACT FROM AUTHOR]