Solar-driven hydrogen fuel electro-generation from water

Abstract

Hydrogen energy, as clean and efficient energy, is considered significant support for the construction of a sustainable society in the face of global climate change and the looming energy revolution. Hydrogen is one of the most important chemical substances on earth and can be obtained through various techniques using renewable and nonrenewable energy sources. However, the necessity for a gradual transition to renewable energy sources significantly hampers efforts to identify and implement green hydrogen production paths. Therefore, this paper’s objective is to provide a technological review of the systems of hydrogen production from solar energy utilizing several types of water electrolyzers. The current paper starts with a short brief about the different production techniques. A detailed comparison between water electrolyzer types and a complete illustration of hydrogen production techniques using solar and wind are presented with examples, after which an economic assessment of green hydrogen production by comparing the costs of the discussed renewable sources with other production methods. One of the main challenges hindering the development of efficient photocathodes is the limited efficiency of the photocathodes themselves, resulting in relatively low current densities being produced. In this context, we bring to light a novel approach that embodies a fresh design principle aimed at enhancing the effectiveness of photocathodes significantly. This innovative approach hinges on the concept of outer-sphere reduction. An intriguing outcome of this methodology is observed when dioxygen is directly reduced from dye-sensitized nickel oxide (NiO), leading to the generation of hydrogen peroxide (H2O2). The experimental results demonstrate that under conditions involving oxygen and visible light, NiO photocathodes sensitized approaching the thermodynamic potential for generation of O2/H2O2 in nearly neutral water. This achievement marks a significant milestone, positioning these particular NiO photocathodes as one of the most efficient reported thus far for multiproton /multielectron transformations. The photoelectrosynthesis mechanism is initiated with the generation of superoxide, which subsequently undergoes disproportionation to yield H2O2. The effectiveness of this disproportionation-driven charge separation strategy lies in its ability to circumvent the inherent difficulties associated with separating electron−hole pairs in photo cathodes connected to inner sphere electrocatalysts. Embracing this innovative approach not only addresses existing challenges but also paves the way for novel applications in photoelectron synthesis cells. Finally, the challenges that face the mentioned production methods are illuminated in the current review.