CAS Shanghai Institute of Ceramics Achieves Progress in Piezocatalysis Research

Source: Shanghai Institute of Ceramics, CAS | Apr 07, 2021

Piezoelectric materials possess non-centrosymmetric structures. Under external mechanical force, asymmetric distribution of surface charges can be induced. These enriched non-equilibrium surface charges are capable of triggering electrochemical reactions, enabling the activation of water and oxygen molecules and the generation of reactive oxygen species under mild conditions. As a result, the conversion of energy-related small molecules (O₂, H₂O, CH₄, etc.) can be realized, making piezocatalysis a promising reaction pathway for green chemical synthesis.

Recently, the Research Group of Energy and Environmental Catalytic Materials at the Shanghai Institute of Ceramics, Chinese Academy of Sciences, rationally designed catalytic systems and fabricated a series of semiconductor materials with piezocatalytic effects. They have carried out research on piezocatalytic hydrogen evolution, piezocatalytic hydrogen peroxide production, and piezocatalytic methane conversion, and revealed the activation and transformation mechanisms of energy-related small molecules on catalyst surfaces. This study is of great significance for converting energetic small molecules into green energy using natural and artificial vibrational energy.

Under ultrasonic irradiation, an ultrathin MoS₂ sheet generates a piezopotential field. With the increase of ultrasonic energy, the built-in electric field inside the material is strengthened and the carrier separation efficiency is improved. Accordingly, the hydrogen evolution rate of MoS₂ rises substantially upon higher ultrasonic input. Electro-modification and surface polarization engineering of MoS₂ not only create extra surface active sites where electrons separated by the built-in electric field accumulate together with H⁺ to further boost hydrogen production, but also introduce hole-trapping sites to facilitate carrier separation, achieving a high hydrogen evolution rate of approximately 1250 μmol·g⁻¹·h⁻¹. This concept coupling piezoelectric effect and catalysis provides a new strategy for semiconductor catalysis and nano energy-conversion devices, and is expected to broaden the application scope of piezoelectric materials in catalysis. The relevant results were published in Journal of Materials Chemistry A, 2018, 6, 11909–11915.

Piezo-response of BiOCl, C₃N₄ and other materials was characterized by piezoresponse force microscopy, and their piezocatalytic active sites were verified via redox reactions of relevant metal ions. When aqueous suspensions of BiOCl or C₃N₄ are sonicated in air, H₂O₂ is produced at rates of 28 μmol/h and 34 μmol/h, respectively. These values exceed those obtained from the corresponding photocatalytic processes, demonstrating stronger catalytic activation of oxygen molecules under the piezopotential field and promising potential for further development of piezocatalysis. The corresponding works were published in ChemSusChem, 2018, 11, 527–531 and Journal of Materials Chemistry A, 2018, 6, 8366–8373.

Taking advantage of the piezocatalytic effect of hydroxyapatite (HAp), methane was converted into low-carbon alcohols through a tandem process combining methane oxidation and methanol coupling. Adsorption of probe molecules and Au³⁺ reduction confirmed that the dominant mechanism under sonication is piezocatalysis rather than sonocatalysis. Upon ultrasonic vibration, induced surface charges on HAp act as surface cathodes and anodes to initiate electrochemical reactions and activate methane, oxygen and water molecules. Hydroxyl radicals generated from activated O₂ and H₂O attack the C–H bonds of methane to form low-carbon alcohols. The piezocatalytic conversion of methane over HAp yields methanol, ethanol and isopropanol at rates of 84.4, 43.2 and 9.6 μmol·g⁻¹·h⁻¹, respectively, without CO or CO₂ formation. This work extends the methane conversion pathway via C–C coupling and suppresses over-oxidation of methanol. Meanwhile, it presents a piezocatalysis-based route for upgrading C₁ species. The relevant results were published in Nano Energy, 2021, 79, 105449.

ezocatalytic hydrogen evolution, piezocatalytic hydrogen peroxide production, and piezocatalytic methane conversion, and revealed the activation and transformation mechanisms of energy-related small molecules on catalyst surfaces. This study is of great significance for converting energetic small molecules into green energy using natura

This research was supported by the National Natural Science Foundation of China.

(a) Schematic illustration of piezocatalytic methane conversion over HAp; (b) Effect of ultrasonic power on conversion efficiency; (c) Ferroelectric hysteresis loop and field-induced displacement curve of HAp.