Human being cannot live without fuel. However, to get clean and renewable fuel is a big challenge to the sustainability of human society. Artificial photosynthesis affords a method to obtain renewable fuels. Herein we trace the history of fuel and solar fuels, present a brief overview on solar water splitting for hydrogen production and CO₂ photo-reduction for chemicals synthesis. Some proposals related to energy policy are discussed in the end of the paper.

Solar-to-chemical energy conversion is one of the most promising solutions to sustainable energy and environmental remedy issues, which has attracted increasing attention both in fundamental research and industrial application. In this review, we choose the key reaction in solar-to-chemical conversion, photocatalytic water splitting, as an example to introduce fundamental scientific advances in this field. We focus on the mechanism of photocatalytic water splitting, light-absorbing materials, photogenerated charge separation, dual-cocatalyst, Z-scheme and technical and economic evaluation of hydrogen production for potential applications. Finally, we present conclusion remarks and future directions of photocatalytic water splitting for solar energy conversion.

Artificial photosynthetic hydrogen evolution is a promising way for solar-to-fuel conversion, which is considered as an important means to solve human energy crisis and environmental pollution. This article reviews the progress of quantum dot artificial photosynthesis hydrogen evolution system, focusing on the analysis of hydrogen evolution efficiency, including quantum dots with hydrogenase mimics, transition metal, and sensitized photocathodes. Specifically, we point out that the capture of photogenerated charges (electrons and holes) plays a pivotal role in improving hydrogen evolution efficiency, and look forward to the development direction of artificial photosynthesis.

Photoelectrocatalytic (PEC) water splitting for H₂ production and CO₂ reduction for fuel production are important ways for solar energy conversion and utilization. However, the PEC efficiency is limited by problems such as poor light absorption, high overpotential and sluggish kinetics of surface reaction, and serious recombination of photogenerated carriers. Herein, we describe the principles of PEC water splitting and CO₂ reduction, recent progress and strategies on increasing the PEC efficiency, including enhancing light absorption via energy band engineering, morphology control and sensitizing strategy, promoting surface reaction via loading cocatalyst, enhancing charge separation and transfer via introducing local dipole and heterojunction electric field, morphology control, interface engineering, etc.

Utilizing sunlight to split water into hydrogen and oxygen is an ideal way to convert solar energy into chemical energy and solve energy and environmental problems. In general, water splitting is hindered by the oxidation of water to oxygen which involves transfer processes of four electrons and four protons. To overcome this obstacle, an effective, robust and low-cost water oxidation catalysts (WOCs), and the anodes and photoanodes that perform fast oxygen evolution at low onset potentials, as well as benign conditions are highly desired. In this article we review recent advances in molecular water oxidation catalysts based on the first-row transition metal elements and advances in commonly used semiconductor materials such as α-Fe₂O₃, WO₃, and BiVO₄. Finally, we briefly discuss the assembly methods (covalent link, π-π stack, etc.) of molecular catalysts to electrodes and the classic examples of anode in catalytic oxidation of water.

Artificial photosynthesis for solar fuels, one of the most important pathways to address energy and environmental issues, has given rise to extensive attentions. Natural photosynthesis that conducts an efficient solar-to-chemical energy conversion has been the inspiration for developing artificial photosynthetic systems for solar fuel production. Based on the scientific issues of natural and artificial photosynthesis, in this article we first review the primary process of solar conversion and CO₂ fixation of natural photosynthesis. Then we focus on the natural-artificial hybrid system which integrates photosynthetic protein, enzyme and whole cell of artificial materials for solar fuel production. Through the coupling of natural and artificial photosynthesis, we reveal the fundamental of solar energy conversion in natural photosynthesis, which can provide us insights into the development of efficient artificial photosynthetic systems.

Artificial photosynthesis for solar fuels production is considered to be an energy disruptive technology in the future, which can fundamentally change the current situation of excessive utilization on fossil fuels. In addition, artificial photosynthesis is an interdisciplinary science involving many fields such as chemistry, physics, materials and biology, and is also a key scientific problem in fundamental science that attracts increasing worldwide interest. In this paper we briefly introduce the concept and key reactions of artificial photosynthesis and focus on the discussion of scalable solutions to solar hydrogen production via water splitting and corresponding technical feasibility analysis. Then we present an introduction and technique routes of liquid solar fuels (e. g. methanol), as well as their potential applications. Finally, we propose a feasible solution to mimick natural artificial process via the coupling of ‘light reaction’ and ‘dark reaction’ for large-scale solar fuels production.

Carbon dioxide is one of the most important greenhouse gases that cause global climate change. Reducing carbon dioxide emissions and converting it to chemicals and fuels with high-value are of great significance for sustainable development. Carbon dioxide hydrogenation to methanol utilizing green hydrogen produced from renewable resources such as solar energy is one of the important ways to solve the greenhouse effect and develop green energy. In recent years, non-copper-based catalysts represented by solid solutions have developed rapidly, showing good industrial application prospects. This paper reviews the research progress of non-copper-based catalysts for selective hydrogenation of carbon dioxide to methanol, with focuses on supported metal catalysts, bimetallic catalysts, solid solution catalysts, and indium oxide-based catalysts, so as to provide references for the design of efficient and stable methanol synthesis catalysts.

Artificial photosynthesis, which converts solar energy to chemical energy, is an important strategy for solar energy utilization. Efficient separation of photoinduced electrons and holes is a key issue in artificial photosynthesis. To investigate the photoinduced electrons and holes using techniques of high temporal and spatial resolutions is crucial to the photo(electro) catalytic mechanism study. This review summarizes the main results and latest development in photo(electro)catalytic mechanism research with time-resolved spectroscopy and imaging spectroscopy. It is shown that charge separation, recombination and reaction process are well characterized by time-resolved spectroscopy while the spatial distribution of photogenerated charges and their roles in artificial photosynthesis are revealed by imaging spectroscopy.