Fast and Stable Electrochemical Production of H₂O₂ by Electrode Architecture Engineering

Abstract

Fast and stable production of hydrogen peroxide (H 2 O 2 ) through electrochemical pathways is crucial for wastewater treatment applications. With this objective, herein, we report an integrated and superaerophilic electrode composed of atomically dispersed Ni−O−C site-enriched carbon nanosheets (IS-NiOC electrode) for electrochemical oxygen reduction to produce H 2 O 2 . Both experimental and theoretical results have proven that atomically dispersed Ni−O−C sites enable a low overpotential (260 mV at 0.1 mA cm −2 ) and high selectivity (>90% at 0.0−0.5 V vs reversible hydrogen electrode (RHE)) in a neutral electrolyte. Compared with a commercial gas-diffusion electrode, the IS-NiOC electrode offers stronger affinity to oxygen bubbles and more robust three-phase contact points, resulting in high current density (∼106 mA cm −2 at 0.25 V vs RHE) and superior stability (∼200 h). These merits allow the application of the IS-NiOC electrode in an electro-Fenton-like process, which enables fast degradation of representative organic pollutants in both a steady state and a flow state.

Tafel Analysis Guided Optimization of ZnNP-O-C Catalysts for the Selective 2-Electron Oxygen Reduction Reaction in Neutral Media

“…Furthermore, the prominent stability (Figure S10) and outstanding performance in a practical electrolysis system (Figures S11–S13) demonstrated the great potential for industrial applications. It is worth noting that, compared with previously reported catalysts in a neutral system, − ,− the M-Zn NP -O-C catalyst still ranked among the best in terms of both catalytic merits (Table S1) and Tafel−θ analysis (Figures e and S14).…”

“…According to the previous studies, − , we hypothesized that the carbon sites adjacent to the metallic Zn nanoparticle and bridging oxygen would have an optimized electronic structure and be active sites for the 2e – ORR. To prove this assumption, we first utilized thiocyanide (SCN – ) to poison metal Zn sites (Figure S21), and the results demonstrated that the activity of M-Zn NP -O-C was almost unchanged after the addition of SCN – ; the active sites for the 2e – ORR are the carbon sites rather than the metal sites.…”

“…Rational structure and composition designation are the key factors to fabricate superior catalysts for 2e – ORRs. In previous studies, various catalysts, including metal-free heteroatom-doped carbon materials , and transition-metal-doped carbon materials, − usually exhibited unsatisfactory performance with either high selectivity (>80%) and mediocre activity (onset potential of <0.53 V vs RHE) or excellent activity (onset potential of ∼0.7 V vs RHE) and low selectivity (<70%) in neutral systems. − Generally, in order to optimize the activity and the selectivity, it is crucial to regulate the adsorption/desorption energy of the reaction intermediate (*OOH), as the weak *OOH adsorption strength leads to poor activity, while the strong adsorption strength causes further reduction to *OH (i.e., low selectivity of H 2 O 2 ). − The conventional electrochemical characterizations (e.g., polarization curves and K–L curves) are commonly used to evaluate catalytic activity and selectivity, while the evaluation of adsorption/desorption energies between the active sites and intermediates is highly dependent on structural characterizations and further theoretical simulations. − ,− Although the aforementioned strategy can be a guide to assess the catalyst, precise structural characterizations (e.g., aberration-corrected transmission electron microscopy and synchrotron radiation) and theoretical simulations are usually time-consuming and labor-intensive. Therefore, in the endeavor of discovering new catalysts for 2e – ORR in neutral media, a fast and accurate evaluation method is urgently needed.…”

Regulating the Surface Electronic Structure of RuNi Alloys for Boosting Alkaline Hydrogen Oxidation Electrocatalysis

“…X-ray photoelectron spectroscopy (XPS) full spectra confirm the existence of Ni 2p, Ru 3p, O 1s, C 1s, and Ru 3d for O-RuNi@C-T (Figure S9 in the Supporting Information). Two peaks (see Figure b, as well as Figure S10 in the Supporting Information) at ∼856.01 and 853.24 eV belong to the 2p 3/2 peaks of Ni 2+ and Ni 0 , respectively. − Compared with Ni@C-400 (Figure S11 in the Supporting Information), the Ni 0 peak for O-RuNi@C-400 negatively shifts ∼0.11 eV (Figure S12 in the Supporting Information), demonstrating the existence of the electron transfer from Ni to Ru. Besides, with the increase of carbonization temperature, the Ni 0 peak negatively shifts, and the peak intensity of Ni 2+ weakens, which is due to the fact that the ratio of Ni–O bond decreases.…”

“…2 eV correspond to C−O−C, C�O, and Ni−O−C, respectively 30,38. As shown in O 1s spectrum of Ni@C-400, we can see the Ni−O−C peak, but compared to O-RuNi@C-400, the Ni−O−C peak is relatively weak.…”