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Electrochemical production of hydrogen peroxide (H2O2) through two‐electron (2 e−) oxygen reduction reaction (ORR) is an on‐site and clean route. Oxygen‐doped carbon materials with high ORR activity and H2O2 selectivity have been considered as the promising catalysts, however, there is still a lack of direct experimental evidence to identify true active sites at the complex carbon surface. Herein, we propose a chemical titration strategy to decipher the oxygen‐doped carbon nanosheet (OCNS900) catalyst for 2 e− ORR. The OCNS900 exhibits outstanding 2 e− ORR performances with onset potential of 0.825 V (vs. RHE), mass activity of 14.5 A g−1 at 0.75 V (vs. RHE) and H2O2 production rate of 770 mmol g−1 h−1 in flow cell, surpassing most reported carbon catalysts. Through selective chemical titration of C=O, C−OH, and COOH groups, we found that C=O species contributed to the most electrocatalytic activity and were the most active sites for 2 e− ORR, which were corroborated by theoretical calculations. [ABSTRACT FROM AUTHOR]

[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]

[Display omitted] • The method of improving dispersion of indium polyphthalocyanine (InPPc) has been proposed. • The sodium dodecylbenzenesulfonate (SDBS) modification induces the matched surface hydrophilicity of carbon nanotubes (CNT) with InPPc. • The InPPc/SDBS@CNT exhibits the increased exposure of active site and electron-deficient In center. Molecular catalysts have emerged as the promising candidate for oxygen reduction to hydrogen peroxide (H 2 O 2). Dispersing homogeneously molecular catalyst on carbon support is the prerequisite for actual electrocatalysis application. Herein, we proposed a novel strategy of modification with sodium dodecylbenzenesulfonate (SDBS) to improve dispersion of indium polyphthalocyanine (InPPc) on carbon nanotube (CNT). The SDBS modification induces the matched surface hydrophilicity of CNT with InPPc, preventing InPPc aggregation. As a result, the InPPc/SDBS@CNT exhibits a remarkable onset potential of 0.84 V vs. RHE and selectivity of > 95 %, superior to InPPc/CNT and most recently reported catalysts. In situ Raman spectrum identifies the critical *OOH intermediate during H 2 O 2 formation on InPPc/SDBS@CNT. Importantly, the InPPc/SDBS@CNT presents a prominent H 2 O 2 production rate of 24.88 mg/cm2/h over 12 h in flow cell. This work provides an effective strategy to promote practical application of molecular catalysts. [ABSTRACT FROM AUTHOR]

The well-designed heterostructured CoP/CN/Ni with oriented electron transfer from the inner Ni to the outer CoP shows excellent electrocatalytic hydrogen evolution and oxygen reduction performances. [Display omitted] • Electronic structure of outer CoP is modulated by the electrons from Ni through CN. • The value of ΔG H* on electron modulated CoP decreases from −0.25 eV to −0.1 eV. • CN layer protects the inner Ni from oxidation and corrosion in harsh environment. • Enriched electrons around CoP weakens its surface oxidation at high potential. Cobalt phosphide (CoP) with its platinum-group-metal like catalytic features has triggered substantial concerns on electrocatalytic hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) under acidic and alkaline conditions. However, the electrocatalytic rate on CoP is restricted because of the reaction intermediates binding to its surface strongly, leading to sluggish reaction kinetics and unsatisfied catalytic performance. Herein, we describe a ternary heterostructured CoP/CN/Ni catalyst with oriented electron modulation effect to boost its electrocatalytic activity, where the electronic structure of the outer CoP is modulated by the endowed electrons from underlying Ni nanoparticles, which are encapsulated and protected by 2–3 N-doped carbon (CN) layers from oxidation and corrosion in harsh environment. Theoretical calculations reveal that the electron redistribution effect could decrease the adsorption energy of hydrogen (ΔG H*) on CoP from −0.25 eV to −0.1 eV. Benefiting from such electron modulation, CoP/CN/Ni only needs overpotentials of 66 mV in 0.5 M H 2 SO 4 and 106 mV in 1 M KOH for HER to afford a current density of 10 mA cm−2 and presents the comparable ORR activity with Pt/C in 0.1 M KOH. Besides, the unique structure also endows CoP/CN/Ni with superior electrocatalytic stability for HER and ORR. [ABSTRACT FROM AUTHOR]