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  1. Abstract

    Photo‐electrochemistry is the major trajectory for directly transforming solar energy into chemical compounds. The performance of a photo‐electrochemical (PEC) system is directly related to the interfacial electrical band energy landscape. Recently, piezotronics has stood out as a promising strategy for tuning interfacial energetics. It applies intrinsic or deformation‐induced ionic displacements (ferroelectric and piezoelectric polarizations) to engineer the interfacial charge distribution, and thereby the band structures of PEC electrodes. Here, contemporary research efforts of coupling piezotronics with photo‐electrochemisty are reviewed. Quantitative band diagrams of a polarization‐tuned semiconductor–electrolyte junction are first introduced, with an emphasis on the impact of interface chemistry. Experimental advances of employing piezoelectric and ferroelectric polarizations to enhance the charge separation and transportation, and surface kinetics of PEC water splitting are discussed. Finally, critical challenges of applying piezotronics in PEC systems and promising solutions are presented.

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  2. null (Ed.)
    A quantitative understanding of the nanoscale piezoelectric property will unlock many application potentials of the electromechanical coupling phenomenon under quantum confinement. In this work, we present an atomic force microscopy- (AFM-) based approach to the quantification of the nanometer-scale piezoelectric property from single-crystalline zinc oxide nanosheets (NSs) with thicknesses ranging from 1 to 4 nm. By identifying the appropriate driving potential, we minimized the influences from electrostatic interactions and tip-sample coupling, and extrapolated the thickness-dependent piezoelectric coefficient ( d 33 ). By averaging the measured d 33 from NSs with the same number of unit cells in thickness, an intriguing tri-unit-cell relationship was observed. From NSs with 3 n unit cell thickness ( n = 1 , 2, 3), a bulk-like d 33 at a value of ~9 pm/V was obtained, whereas NSs with other thickness showed a ~30% higher d 33 of ~12 pm/V. Quantification of d 33 as a function of ZnO unit cell numbers offers a new experimental discovery toward nanoscale piezoelectricity from nonlayered materials that are piezoelectric in bulk. 
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  3. null (Ed.)
    Creating two-dimensional (2D) geometry from nonlayered catalytic materials may significantly advance electrocatalyst design. The 2D morphology of three-dimensional lattices (2D nonlayered materials) offer large structural distortions, massive surface dangling bonds, and coordinated-unsaturated surface atoms, which can induce high surface chemical activity and promote the chemisorption of reactants and fast interfacial charge transfer, thereby enhancing the electrocatalytic performance. In this article, we review typical strategies for structural engineering and manipulation of electronic states to enable the unique electrocatalytic advantages of 2D nonlayered materials. An overview is presented on recent research advances in the development of 2D nonlayered materials for catalyzing the representative electrochemical reactions that are essential to energy and sustainability, including hydrogen evolution, oxygen evolution, oxygen reduction, and CO 2 reduction. For each type of redox reactions, their unique catalytic performance and underlying mechanism are discussed. Important achievements and key challenges are also discussed. 
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  4. null (Ed.)
    As a promising technology for sustainable hydrogen generation, photocatalytic (PC) and photoelectrochemical (PEC) water splitting have gathered immense attention over a half-century. While many review articles have covered extensive research achievements and technology innovations in water splitting, this article focuses on illustrating how the ferroelectric polarization influences charge separation and transportation in photocatalyst heterostructures during PC and PEC water splitting. This article first discusses the fundamentals of PC and PEC water splitting and how these electrochemical processes interact with the ferroelectric polarization-induced interfacial band bending, known as piezotronics. A few representative ferroelectric material-based heterogeneous photocatalyst systems are then discussed in detail to illustrate the effects of polarization, space charge region, and free charge concentration, which are critical factors determining the ferroelectric influences. Finally, a forward looking statement is provided to point out the research challenges and opportunities in this promising interdisciplinary research field between ferroelectrics and electrochemistry for clean energy applications. 
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  5. null (Ed.)