Unassisted self-healing photocatalysts based on Le Chatelier's principle

Abstract

Self-healing is a fundamental ability inherent in humans, plants, and other living organisms. To date, a variety of materials with self-healing properties have been developed. However, these materials usually require external inputs such as electric potentials or healing agents to initiate or promote self-healing reactions. Herein, we present a novel self-healing mechanism that operates without any external input, utilizing the dynamic equilibrium between the solid-state and dissolved materials. We employed organic-inorganic perovskites to validate our strategy. Single-particle spectroscopy and imaging demonstrated the spontaneous self-healing of perovskites after photodamage under dynamic equilibrium conditions. Furthermore, we found that perovskites can generate hydrogen in both healed and damaged states. Remarkably, the perovskites exhibited hydrogen generation over four cycles of photodamage and self-healing. The proposed concept and experimental results provide valuable insights for the development of energy conversion and storage systems with improved long-term durability.

Fig. 1. Overview of self-healing reactions based on Le Chatelier’s principle.

a Comparison of self-healing mechanisms. (i) Conventional self-healing materials such as polymers, glasses, and metals. (ii) Self-healing (photo)catalysts such as photoelectrodes and air-reactive catalysts. (iii) Our newly developed self-healing system. In the system, self-healing reactions on the material occur spontaneously without external inputs. b Schematic illustration of self-healing mechanism based on Le Chatelier’s principle. When equilibrium is disturbed due to material damage (first step), the reaction system tends to shift to mitigate the disturbance (second step). Following the completion of the self-healing process, the reaction system returns to equilibrium (third step).

Fig. 2. Single-particle observations using microscopic techniques.

a Experimental setup for single-particle measurements. The experimental setup is based on a wide-field fluorescence microscope system. Both PL and transmitted light were captured using the same objective lens. b–f Optical images of mixed-halide MAPbBr_xI_3−x perovskites with various x-values in aqueous solution. g–k Optical transmission images in aqueous solution. The inset labels indicate the time after the start of photoirradiation. Excitation was provided for the first 300 s, after which photoirradiation was stopped. A 405-nm CW laser (ca. 780 mW·cm⁻² at the sample surface) was used as the excitation source.

Fig. 3. Damaging and self-healing reactions of perovskites.

Optical transmission and PL images of MAPbBr_2.8I_0.2 in aqueous solution before (a) and during photoirradiation (b–d). The inset labels show the time elapsed from the start of light irradiation. A 405-nm CW laser (ca. 1.21 W·cm⁻² at the sample surface) was used as the excitation source. e Spectral changes of the MAPbBr_2.8I_0.2 crystal in aqueous solution under irradiation. A 405-nm pulsed laser (ca. 8×10⁻¹⁷ J·pulse⁻¹) was used as excitation source. f Schematic illustration of the crystal destruction mechanism induced by halide phase segregation. g Pb 4 f XPS spectra of MAPbBr_2.8I_0.2 before and after irradiation, and after self-healing. A 405-nm LED (ca. 350 mW·cm⁻²) was used as excitation source. h XRD patterns of MAPbBr_2.8I_0.2 in aqueous solution before and after irradiation. A 405-nm LED (ca. 350 mW·cm⁻²) was used as excitation source. Asterisks indicate characteristic peaks of metallic Pb (PDF card: 00-004-0686). i Temporal changes in the Pb⁰ peak area under irradiation (yellow-shaded region) and after stopping irradiation (gray-shaded region). The error bars represent the standard deviation.

Fig. 4. (Photo)catalytic hydrogen-production activity of perovskites under visible-light irradiation in aqueous solution.

a Optical images of the MAPbBr_2.8I_0.2 powder in saturated aqueous solution (left) before and (right) after 470-nm LED light irradiation (ca. 125 mW·cm⁻²) for 24 h. b Total amount of hydrogen generated by perovskites, indicating the catalytic activity of MAPbBr₃ (black line and symbols), MAPbI₃ (red line and symbols), MAPbBr_1.3I_1.7 (purple line and symbols), MAPbBr_2.2I_0.8 (green line and symbols) and MAPbBr_2.8I_0.2 (blue line and symbols). The yellow-shaded region indicates the period of light irradiation, while the gray-shaded region indicates the period of darkness. c The hydrogen production of MAPbBr_2.8I_0.2 during intermittent irradiation. d Schematic illustration of degradation and self-healing reactions in aqueous solution under dynamic equilibrium. The self-healing reaction occurs spontaneously once the perovskites are damaged, and this cycle can continue repeatedly.