(Invited) On the Anisotropic Charge Separation and the Growth of Highly Ordered Heteronanostructures for Efficient Photocatalytic Water Splitting

Abstract

A sustainable hydrogen-based energy source combined with existing renewable energy sources such as photovoltaics and wind and tidal wave power is the ideal scenario for the future of our societies as it produces zero carbon emission, only water[1]. Unfortunately, most of the hydrogen industrially produced nowadays still comes from nonrenewable resources, typically from methane steam reforming which produces considerable amount of carbon monoxide and dioxides along with the hydrogen. So currently, hydrogen is very clean to use but still very dirty to produce. The most natural and cleanest way to sustainably produce hydrogen at large scale is by splitting water photo(electro)catalytically. Consequently, a great increase in research during the past decade, with dedicated efforts on material design and surface and electronic structure engineering have been conducted to identify ideal materials and systems[2]. Our own strategy includes the fabrication of low-cost earth-abundant heteronanostructures consisting of highly oriented arrays of quantum rods and dots of high purity synthesized by aqueous chemical growth at low temperature without surfactant and with controlled dimensionalities and surface chemistry[3] with intermediate bands for high visible-light conversion, bandgap and band edges optimized for stability against photocorrosion and operation conditions at neutral pH and low or no bias without sacrificial agent. Such unique characteristics, combined with the in-depth investigation of their size-dependent, interfacial electronic structure[4], defect chemistry and electrical conductivity effects[5] do provide better fundamental understanding and direct structure-efficiency relationships for a cost-effective and sustainable generation of clean hydrogen from the two most abundant and geographically-balanced free resources on earth’s surface, e.g. the sun and seawater. An overview of the past decades progress along with the latest advances in the controlled fabrication of environmental-friendly highly ordered heteronanostructures by anisotropic charge separation[6] for stable and efficient (sea)water splitting will be presented. [1] Y. Tachibana et al. Nat. Photon. 2012, 6, 511 [2] X. Guan et al. ACS Energy Lett. 2018, 3, 2230; J. Phys. Chem. C 2018, 122, 13797; J. Su et al, J. Phys. Chem. Lett. 2017, 8, 5228; ACS Energy Lett. 2016, 1, 121; C.X. Kronawitter et al., Energy Environ. Sci. 2011, 4, 3889. [3] L.Vayssieres, Int. J. Nanotechnol. 2005, 2, 411; J. Phys. Chem. C 2009, 113, 4733; Adv. Mater. 2003, 15, 464; Angew. Chem. Int. Ed. 2004 , 43(28), 3666; Int. J. Nanotechnol. 2004, 1, 1. [4] C.L. Dong et al. Chem Eur. J. 2018, 24, 18356; M.G. Kibria et al. Adv. Mater. 2016, 28, 8388; L.Vayssieres et al. Appl. Phys. Lett. 2011 99, 183101; Adv. Mater. 2005, 17, 2320; C.X. Kronawitter et al. Phys. Rev. B 2012, 85, 125109; Energy Environ. Sci. 2014, 7, 3100; Nano Lett. 2011, 11, 3855; J. Phys. Chem. C 2012, 116, 22780; PhysChemChemPhys 2013, 15, 13483. [5] J. Wang et al. ACS Appl. Mater. Interfaces 2019, 11, 2031; J. Engel et al. Adv. Func. Mater. 2014, 24, 4952. [6] Y.Wei et al. Nano Res. 2016, 9, 1561; K. Nie et al. Nano Energy 2018, 53, 483; L. Wang et al. Nano Res. 2019, 12, 575; Z. Q. Wang et al. J. Electrochem. Soc. 2019, 166, H3138.