Significance It is well known that energy, material, and information have been regarded as the three cornerstones of human civilization and social development. The exploitation and utilization of energy by human beings has continued through human evolution without interruption. Fossil fuels, including coal, oil, and natural gas, have promoted tremendous social change and brought inestimable value to human beings. Traditional fossil fuels are non-renewable energy sources with limited reserves in the earth's crust. Excessive exploitation without replacement or alternative energy sources will inevitably lead to fossil fuel depletion. Due to increasing environmental pollution, humans begin to realize environmental hazards caused by the excessive use of fossil fuels, such as global warming, acid rain, and particulate matters. With respect to severe energy and environmental crises, it is imperative to develop green and clean energy technologies to reduce the use of increasingly exhausted fossil fuels and achieve environmentally-friendly and sustainable social developments. Hydrogen, as a renewable energy carrier, has attracted significant attention due to the following four reasons. First, hydrogen is a clean and low-carbon energy carrier and its reaction product is only water with no carbon dioxide emissions. Second, hydrogen has a high calorific value, about three times higher than fossil fuels. Third, hydrogen is widely used in electricity, construction, transportation, and industrial fields. It can be used as a raw material for the steel, metallurgical and chemical industries and as a fuel in fuel cells. Fourth, hydrogen is earth-abundant, which can originate from fossil fuel reforming, water splitting, and by-products of the chlor-alkali industry. Many governments around the world are committed to developing hydrogen energy and arranging relevant industrial chains. The International Renewable Energy Agency pointed out that hydrogen can build a connection among electricity, construction, industry, and transportation to achieve deep decarbonization. Developing various technologies for hydrogen production is important in developing hydrogen energy and the hydrogen economy. Nowadays, there are three main pathways for hydrogen production, namely, methane-steam reforming, coal gasification, and electrocatalytic water splitting. Though the first two pathways account for about 95% of hydrogen production, they still rely on fossil fuels and emit large amounts of carbon dioxide, which violates the goal of developing hydrogen energy. In contrast, electrocatalytic water splitting does not lead to carbon emissions and is a green and sustainable hydrogen production technology. However, electrocatalytic water splitting has shortcomings of excessive energy consumption and high cost, which restricts its large-scale application. Electrocatalytic water splitting contains a cathodic hydrogen evolution reaction (HER) and an anodic oxygen evolution reaction ( OER), both which need efficient electrocatalysts to overcome the high reaction barrier. Therefore, how to improve electrocatalytic performance and reduce electrolytic overpotential are keys in realizing large-scale applications of electrocatalytic water splitting. Over the past few years, various methods have been developed to prepare electrocatalysts for electrocatalytic water splitting, mainly including the hydrothermal/solvothermal method, sol-gel method, electrochemical deposition, chemical bath deposition, chemical vapor deposition, and physical vapor deposition. Specifically, lasers have become an effective tool to prepare catalysts for electrocatalytic water splitting with advantages of being efficient, flexible, contactless, and highly controllable. Many corresponding advances have been achieved, but they still face a series of challenges in terms of industrial feasibility and performance improvement. Hence, it is important and necessary to summarize the existing research to guide the future development of this field more rationally. Progress Preparation methods of electrocatalysts for electrocatalytic water splitting based on lasers and their catalytic performances have been summarized. First, the implementation process of electrocatalytic water splitting, evaluation parameters, classification, and preparation methods of electrocatalysts are introduced. The evaluation parameters include overpotential, Tafel slope, stability, Faraday efficiency, and turnover frequency. Then, the catalytic performances of electrocatalysts prepared by laser are comprehensively summarized according to previously reported studies. Subsequently, powder catalysts by laser in liquid and self-supported catalytic electrodes with micronano structures by laser are elaborated. Considering the interaction mechanism, the preparation process of powder catalysts by laser can be divided into laser irradiation in liquid and laser ablation in liquid. Haimei Zheng's research group from University of California, Berkeley, has pioneered laser irradiation in liquid. Xiwen Du's research group from Tianjin University has engaged in plenty of systematic studies on laser ablation in liquid. Based on the preparation method, the preparation process of self-supported catalytic electrodes with micro-nano structures by laser can be divided into laser direct preparation and laser hybrid with other chemical synthesis methods. Currently, studies of self-supported catalytic electrodes by laser are limited and incomprehensive. In the end, the problems faced and ongoing research trends in this field are discussed, including the type of laser, the characterization and theoretical calculation of catalysts, the design of bifunctional catalysts, and the performance evaluations at industrial conditions. Conclusion and Prospect Lasers are gradually becoming a popular tool to prepare various functional materials. In summary, the preparation of micro -nano catalysts for electrocatalytic water splitting by laser still needs in-depth and detailed exploration to promote the development of this hydrogen production technology in academic and engineering aspects.
