Directionally tailoring the macroscopic polarization of piezocatalysis for hollow zinc sulfide on dual-doped graphene

Inefficient mechanical energy capture and inadequate active sites of piezoelectric materials remain the principal impediment for more widespread application in environmental remediation. Herein, a strategy was proposed to substantially improve the piezocatalytic performance via hybridizing hollow wurtzite ZnS nanospheres (H-ZnS) onto flexible S,N-codoped graphene (SNG). The resulting piezoelectric composite (H-ZnS@SNG) exhibited faster electrical transport and more superior piezocatalytic properties for dye degradation (~100% in 10 min) under external strain (either ultrasonic or mechanical stirring), compared with bulk H-ZnS (~58.4%) and the piezoelectric composite coupled with solid wurtzite ZnS nanospheres (S-ZnS@SNG, ~89.9%). This improvement is ascribed to the strain-induced piezopolarization charges of H-ZnS@SNG, with the unique hollow structure of the H-ZnS nanosphere accelerating the electron transfer of heterogeneous graphene. H-ZnS@SNG had the optimum crystal phase and morphology of H-ZnS at the annealing treatment temperature of 700 ℃, leading to the highest piezocatalytic performance. Simulations of the wurtzite hollow ZnS piezocatalyst ties the enhanced performance to excellent flexibility, along with more catalytic active sites on both inner and outer surfaces, compared with solid ZnS. This study provides valuable insights into the mechanisms underlying the excellent purification efficiency by hollow structural piezocatalysts, which are expected to be useful in customizing the designs of such materials for practical implementation.Agency for Science, Technology and Research (A*STAR)Ministry of Education (MOE)This work was supported by the National Natural Science Foundation of China (Grant No. 22076169), A*STAR (Singapore) Advanced Manufacturing and Engineering (AME) under its Individual Research Grant (IRG) program (A2083c0049), the Singapore Ministry of Education Academic Research Tier 1 Grant (2019-T1–002-065; RG100/19) and the Singapore Ministry of Education Academic Research Tier 2 Grant (MOE-MOET2EP10120–0001)

Highly Stable and Efficient Catalyst with In Situ Exsolved Fe–Ni Alloy Nanospheres Socketed on an Oxygen Deficient Perovskite for Direct CO₂ Electrolysis

The massive emission of carbon dioxide (CO₂), the major portion of greenhouse gases, has negatively affected our ecosystem. Developing new technologies to effectively reduce CO₂ emission or convert CO₂ to useful products has never been more imperative. In response to this challenge, we herein developed novel in situ exsolved Fe–Ni alloy nanospheres uniformly socketed on an oxygen-deficient perovskite [La­(Sr)­Fe­(Ni)] as a highly stable and efficient catalyst for the effective conversion of CO₂ to carbon monoxide (CO) in a high-temperature solid oxide electrolysis cell (HT-SOEC). The symmetry between the reduction and reoxidation cycles of this catalyst indicates its good redox reversibility. The cathodic reaction kinetics for CO₂ electrolysis is significantly improved with a polarization resistance as low as 0.272 Ω cm². In addition, a remarkably enhanced current density of 1.78 A cm^–2, along with a high Faraday efficiency (∼98.8%), was achieved at 1.6 V and 850 °C. Moreover, the potentiostatic stability test of up to 100 h showed that the cell was stable without any noticeable coking in a CO₂/CO (70:30) flow at an applied potential of 0.6 V (vs OCV) and 850 °C. The increased oxygen vacancies together with the in situ exsolved nanospheres on the perovskite backbone ensures sufficiently active sites and consequently improves the electrochemical performance for the efficient CO₂ conversion. Therefore, this newly developed perovskite can be a promising cathode material for HT-SOEC. More generally, this study points to a new direction to develop highly efficient catalysts in the form of the perovskite oxides with perfectly in situ exsolved metal/bimetal nanospheres

Efficient electrochemical reduction of CO2 to HCOOH over Sub-2 nm SnO2 quantum wires with exposed grain boundaries

Electrochemical reduction of CO2 could mitigate environmental problems originating from CO2 emission. Although grain boundaries (GBs) have been tailored to tune binding energies of reaction intermediates and consequently accelerate the CO2 reduction reaction (CO2 RR), it is challenging to exclusively clarify the correlation between GBs and enhanced reactivity in nanostructured materials with small dimension (<10 nm). Now, sub-2 nm SnO2 quantum wires (QWs) composed of individual quantum dots (QDs) and numerous GBs on the surface were synthesized and examined for CO2 RR toward HCOOH formation. In contrast to SnO2 nanoparticles (NPs) with a larger electrochemically active surface area (ECSA), the ultrathin SnO2 QWs with exposed GBs show enhanced current density (j), an improved Faradaic efficiency (FE) of over 80 % for HCOOH and ca. 90 % for C1 products as well as energy efficiency (EE) of over 50 % in a wide potential window; maximum values of FE (87.3 %) and EE (52.7 %) are achieved.NRF (Natl Research Foundation, S’pore)Accepted versio

Rational Design of Silver Sulfide Nanowires for Efficient CO₂ Electroreduction in Ionic Liquid

Electroreduction of CO₂ holds the promise for the utilization of CO₂ and the storage of intermittent renewable energy. The development of efficient catalysts for effectively converting CO₂ to fuels has never been more imperative. Herein, we successfully synthesized Ag₂S nanowires (NWs) dominating at the facet of (121) using a modified facile one-step method and utilized them as a catalyst for electrochemical CO₂ reduction reaction (CO₂RR). Ag₂S NWs in ionic liquid (IL) possess a partial current density of 12.37 mA cm^–2, ∼14- and ∼17.5-fold higher than those of Ag₂S NWs and bulk Ag in KHCO₃, respectively. Moreover, it shows significantly higher selectivity with a value of 92.0% at the overpotential (η) of −0.754 V. More importantly, the CO formation begins at a low η of 54 mV. The good performance originates from not only the presence of [EMIM–CO₂]⁺ complexes but also the specific facet contribution. The partial density of states (PDOS) and work functions reveal that the d band center of the surface Ag atom of Ag₂S­(121) is closer to the Fermi energy level and has a higher d-electron density than those of Ag(111) and Ag55, which lowers transition state energy for CO₂RR. Besides, density functional theory (DFT) calculations indicate that the COOH* formation over Ag₂S is energetically more favorable on (111) and (121) facets than that on Ag(111) and Ag55. Therefore, we conclude that the significantly enhanced performance of Ag₂S NWs in IL synergistically originates from the solvent-assisted and specific facet-promoted contributions. This distinguishes Ag₂S NWs in IL as an attractive and selective platform for CO₂RR

Shape-Dependent Electrocatalytic Reduction of CO₂ to CO on Triangular Silver Nanoplates

Electrochemical reduction of CO₂ (CO₂RR) provides great potential for intermittent renewable energy storage. This study demonstrates a predominant shape-dependent electrocatalytic reduction of CO₂ to CO on triangular silver nanoplates (Tri-Ag-NPs) in 0.1 M KHCO₃. Compared with similarly sized Ag nanoparticles (SS-Ag-NPs) and bulk Ag, Tri-Ag-NPs exhibited an enhanced current density and significantly improved Faradaic efficiency (96.8%) and energy efficiency (61.7%), together with a considerable durability (7 days). Additionally, CO starts to be observed at an ultralow overpotential of 96 mV, further confirming the superiority of Tri-Ag-NPs as a catalyst for CO₂RR toward CO formation. Density functional theory calculations reveal that the significantly enhanced electrocatalytic activity and selectivity at lowered overpotential originate from the shape-controlled structure. This not only provides the optimum edge-to-corner ratio but also dominates at the facet of Ag(100) where it requires lower energy to initiate the rate-determining step. This study demonstrates a promising approach to tune electrocatalytic activity and selectivity of metal catalysts for CO₂RR by creating optimal facet and edge site through shape-control synthesis

Photo/electrocatalytic hydrogen exploitation for CO2 reduction toward solar fuels production

This chapter discusses the transformation of CO2 to value-added products, with a focus on the exploitation of sun-driven water splitting for generation of hydrogen protons (H+) that can be used in situ for the CO2 reduction reaction. It starts by introducing CO2 as a raw material for the production of fuels or chemicals by conventional (thermocatalytic) conversion processes or emerging sun-driven technologies. It then gives a background about the different figures of merit that must be considered and identifies the opportunities for syngas production. Different architectures for syngas production are presented, considering the photo-driven systems and with particular emphasis on the electrochemical systems. It proceeds by extensively discussing various catalysts for these two kinds of systems. Finally, it tackles the promising solvent-less route for the electrochemical conversion of CO2 to value-added products