# Ferroelectric Materials: A Novel Pathway for Efficient Solar Water Splitting
## 1 Introduction  
In order to effectively address energy-related problems such as global warming, which is caused by the emissions of air pollutants including carbon dioxide (CO\({}_{2}\)), there is a growing interest in many kinds of renewable energy (such as solar, wind power, hydroelectric energy, and biomass), and their related applications as an alternative to fossil fuels [1, 2].  
Among the various alternative energy sources, solar energy is an almost unlimited and clean energy source, given that the Sun has been providing energy in the form of light and heat to the Earth for more than four billion years. Until now, solar energy has been considered as an alternative energy option that could help address several problems of global importance such as an insufficient energy supply, environmental pollution, and fossil fuel resource depletion. Moreover, most regions of our planet including the atmosphere, oceans, and soil receive approximately 3850 zeta joules (ZJ = 10\({}^{21}\) J) of energy every year (-0.539 ZJ of energy was consumed worldwide in 2010). Considering only the amount of energy received from the Sun, solar energy is one of best candidates as a substitution for fossil fuels. Even though many researchers have been actively involved in alternative energy research and related technologies have been developed over the years, no more than 1% of the energy produced by the Sun is used by our planet. Therefore, we need to concentrate on the efficiently of solar energy use, whether indirectly or directly [3, 4]. In particular, for a solar energy carrier, three main points have to be considered. (1) How much cheaper and abundant are chemical reactants? (2) Is the carrier easily stored and transported? (3) In the process, is carbon dioxide generated and emitted?  
On the other hand, hydrogen energy and related applications are considered to be excellent alternative renewable energy carriers due to their storability, transportability, and convertibility to energy on demand. Hydrogen gas is a clean, nontoxic, colorless, and eco-friendly source (does not release carbon dioxide) that could be obtained by splitting naturally occurring water into hydrogenand oxygen. Moreover, hydrogen could be used in various energy applications such as hydrogen fuel cells (HFCs), combustible fuel, and synthetic natural materials. It is known that when the gas is used for electricity production such as in the case of hydrogen-powered fuel cells, it has three times the efficiency of electricity generation (\(\sim\)65%) compared to conventional combustion-based power plants (\(\sim\)35%) [5; 6; 7].  
In order for hydrogen to be classified as an environmentally friendly alternative energy source, it should be produced using appropriate processes that use carbon-free environmentally friendly materials instead of fossil fuels. Compared with other methods of hydrogen production (biomass, thermal decomposition of natural gas, water electrolysis, and thermochemical cycles), water-splitting technology has been proposed as the most suitable method for the eco-friendly generation of hydrogen gas from water. It should be noted that solar energy has been used as an energy conversion source of solar thermal and photovoltaics starting from solar light. In particular, water splitting using photovoltaics based on solar energy is ideal for the generation of hydrogen gas from water [8; 9].  
This review will address solar water-splitting technology (such as water splitting in photosynthesis, photoelectrochemical water splitting, and photocatalytic water splitting), including the systems involved and hydrogen production from water and solar energy. Moreover, we will introduce the recent progress in solar water splitting using ferroelectric materials, and summarize how each material plays an important role in achieving efficient solar water splitting.