Electrocatalytic Water Splitting: From Harsh and Mild Conditions to Natural Seawater

Abstract

Electrocatalytic water splitting is regarded as the most effective pathway to generate green energy—hydrogen—which is considered as one of the most promising clean energy solutions to the world's energy crisis and climate change mitigation. Although electrocatalytic water splitting has been proposed for decades, large‐scale industrial hydrogen production is hindered by high electricity cost, capital investment, and electrolysis media. Harsh conditions (strong acid/alkaline) are widely used in electrocatalytic mechanism studies, and excellent catalytic activities and efficiencies have been achieved. However, the practical application of electrocatalytic water splitting in harsh conditions encounters several obstacles, such as corrosion issues, catalyst stability, and membrane technical difficulties. Thus, the research on water splitting in mild conditions (neutral/near neutral), even in natural seawater, has aroused increasing attention. However, the mechanism in mild conditions or natural seawater is not clear. Herein, different conditions in electrocatalytic water splitting are reviewed and the effects and proposed mechanisms in the three conditions are summarized. Then, a comparison of the reaction process and the effects of the ions in different electrolytes are presented. Finally, the challenges and opportunities associated with direct electrocatalytic natural seawater splitting and the perspective are presented to promote the progress of hydrogen production by water splitting.

Highly Durable and Efficient Ni-FeOx/FeNi3 Electrocatalysts Synthesized by a Facile In Situ Combustion-Based Method for Overall Water Splitting with Large Current Densities

“…Rapidly growing energy consumption, environmental pollution, and prerequisites for future green energy supply have compelled the world to search for substitutes to replace depleting fossil fuels. Hydrogen gas (H 2 ) is an attractive, clean energy source and provides a desirable solution as a carbon-free and high mass–energy density (three times that of gasoline) fuel. − Electrolysis of water in which H 2 /O 2 is generated by the hydrogen evolution reaction (HER)/oxygen evolution reaction (OER) is expected to be widely applied in sustainable and green hydrogen production when it is powered by renewable energy generated by sunlight, wind, running water, ocean energy, etc. − Nevertheless, the unfavorable thermodynamics and sluggish kinetics of common catalysts for HER and OER lead to high electricity consumption and make this technology far from being competitive with commercial coal gasification and steam methane reformation . To accelerate the development, advanced noble metal-based materials such as platinum- and Ru/Ir-derived electrocatalysts with high intrinsic activity are mainly used to lower the overpotential (η) of HER/OER at respective electrodes. − However, the natural scarcity, high cost, and low durability in long-term applications have impeded extensive implementation, and therefore, significant attention has been paid to identifying low-cost, earth-abundant, and efficient electrocatalysts including alloys, oxides, sulfides, nitrides, carbides, phosphides, and hydroxides to replace noble metals. ,− Although progress has been made recently to enhance the efficiency and stability, only a handful of catalysts possess high and stable activities in the same electrolyte in both OER and HER, thereby raising the production cost , and making the electrolyzer relatively complex .…”

Simultaneous optimization of CoIr alloy nanoparticles and 2D graphitic-N doped carbon support in CoIr@CN by Ir doping for enhanced oxygen and hydrogen evolution reactions

“…Hydrogen, a zero-emission material with high energy density, is regarded as an attractive energy carrier to alleviate the serious fossil fuel energy crisis and environmental issues. 1,2 Water electrolysis, consisting of oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), is an effective means to large-scale produce pure hydrogen. Normally, the overall efficiency of water splitting always suffers from high overpotential and sluggish kinetics of the OER and HER, particularly the anodic OER with a four proton-coupled electron transfer process.…”

Hierarchical Metal Sulfides Heterostructure as Superior Bifunctional Electrode for Overall Water Splitting

“…[1][2][3] Electrocatalytic water splitting, which consists of hydrogen evolution reaction (HER) in cathode and oxygen evolution reaction (OER) in anode, is proved to be one of the ways to produce hydrogen energy with high application prospects. [4][5][6][7][8][9] However, the inevitable high potential limits the efficiency of overall water electrolysis, especially for the OER half-reaction with slow four-electron transfer process. [10,11] Therefore, designing electrocatalysts with high catalytic activity is the key to improving their energy efficiency.…”