Compositionally Tuned Trimetallic Thiospinel Catalysts for Enhanced Electrosynthesis of Hydrogen Peroxide and Built-In Hydroxyl Radical Generation

Abstract

On-site electrochemical production of hydrogen peroxide (H2O2), an oxidant and disinfectant with growing demand, could be realized through the selective two-electron oxygen reduction reaction (2e– ORR), but the widespread adoption of this method depends on robust and efficient electrocatalysts. Current catalysts have been limited by cost or toxicity and lack well-defined structures that can facilitate systematic tuning of activity and selectivity. Here, we demonstrate a series of CuCo2–x Ni x S4 (0 ≤ x ≤ 1.2) thiospinel catalysts for 2e– ORR with variable compositions that can be synthesized via hydrothermal conversion. Rotating ring disk electrode measurements show that these catalysts have high selectivity for 2e– ORR (>60%) and that their activity can be improved by increasing the nickel content without compromising selectivity. An acid treatment step is critical prior to employing the optimized CuCo0.8Ni1.2S4 catalyst for bulk electrosynthesis of H2O2 in 0.05 M H2SO4 solution. Various structural analyses, including synchrotron X-ray spectroscopy, confirm that the catalysts retain the spinel structure after acid treatment and H2O2 electrosynthesis. The acid treatment likely leaches the soluble copper species from the as-synthesized catalysts that would catalyze an electro-Fenton process to consume H2O2, generate hydroxyl radicals, and therefore prevent the accumulation of H2O2. This work demonstrates a general strategy for systematic tuning of metal compound catalysts for practical H2O2 electrosynthesis and facile generation of hydroxyl radicals.

Identification of the Highly Active Co–N4 Coordination Motif for Selective Oxygen Reduction to Hydrogen Peroxide

“…In recent years, there has been an incremental interest in searching for highly efficient and stable 2e – ORR catalysts in acid environments, including noble-based materials, ,− transitional metal compounds, − single-atom catalysts (SACs), ,− and carbon materials. − Among these, the carbon-based transition metal SAC has received special attention due to its high atom unitization, high electrical conductivity, and adjustable coordination environment . For instance, both Liu et al and Strasser et al have screened different carbon-based transition metal SACs (such as Fe, Co, Ni, Cu, and Mn).…”

Operando Elucidation of Electrocatalytic and Redox Mechanisms on a 2D Metal Organic Framework Catalyst for Efficient Electrosynthesis of Hydrogen Peroxide in Neutral Media

“…11,15 Therefore, it is desirable to control the catalytic active site environments to systematically improve their design for optimized 2e − ORR activity and selectivity. Tunability could be achieved in metal chalcogenide catalysts with well-defined crystal struc- tures, 8,16−20 but these compounds are primarily active in acidic media and sometimes require further post-treatment to improve stability 16 and minimize hazardous metal leaching.…”

“…Single-atom catalysts (SACs) have emerged as promising 2e – ORR catalysts, ,− but the difficulty of characterizing their catalytic active structures hinders their developement because these 2e – ORR SAC catalysts are highly sensitive to the electronic structure of adjacent atomic sites. , Therefore, it is desirable to control the catalytic active site environments to systematically improve their design for optimized 2e – ORR activity and selectivity. Tunability could be achieved in metal chalcogenide catalysts with well-defined crystal structures, ,− but these compounds are primarily active in acidic media and sometimes require further post-treatment to improve stability and minimize hazardous metal leaching.…”

Coupling Co–N–C with MXenes Yields Highly Efficient Catalysts for H2O2 Production in Acidic Media

“…H 2 O 2 can be produced in alkaline/acidic media. ,− Carbon materials are widely studied as catalysts for H 2 O 2 electrosynthesis in alkaline media due to their abundant reserves, morphological and electronic structural diversity, and mechanical and chemical stability. ,− However, the generated H 2 O 2 tends to readily decompose in alkaline media. ,, Therefore, it is more desirable to produce H 2 O 2 in acidic media. At present, the most effective catalysts for H 2 O 2 generation in acidic media are noble metal-based alloys due to their high selectivity and stability. − However, their applications are restricted by the high cost.…”

“…At present, the most effective catalysts for H 2 O 2 generation in acidic media are noble metal-based alloys due to their high selectivity and stability. − However, their applications are restricted by the high cost. Thus, searching for novel noble metal-free two-electron ORR catalysts with high activity is imperative. ,− …”