A binder-free thin film anode composed of Co2+-intercalated buserite grown on carbon cloth for oxygen evolution reaction

Water electrolysis: from textbook knowledge to the latest scientific strategies and industrial developments

Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO2 footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the 'junctions' between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

Layered Manganese Dioxide Thin Films Intercalated with Ag+ Ions Reduceable In Situ for Oxygen Reduction Reaction

The purpose of this study is to propose a new strategy based on electrodeposition to create binder-free composites of metallic silver supported on MnO₂. The process involves in situ reduction of the Ag⁺ ions incorporated in the interlayer spaces of layered MnO₂ in an alkaline electrolyte without Ag⁺ ions. The reduction process of the incorporated Ag⁺ was monitored in situ based on the characteristic surface plasmon resonance in the visible region, and the resulting metallic Ag was identified by X-ray photoelectron spectroscopy. Because the formation of metallic Ag is only possible via electron injection into the Ag⁺ ions between MnO₂ layers, the growth of Ag metals was inevitably limited, although the reduced Ag did not remain immobilized in the interlayers of MnO₂. The thus-formed Ag in the MnO₂ composite functioned as an electrocatalyst for the oxygen reduction reaction in a gas diffusion electrode system, showing a much better mass activity compared to Ag particles electrodeposited from an aqueous solution containing AgNO₃.

NiFe Hydroxide Supported on Hierarchically Porous Nickel Mesh as a High-Performance Bifunctional Electrocatalyst for Water Splitting at Large Current Density

The preparation of efficient and low-cost bifunctional catalysts with superior stability for water splitting is a topic of significant current interest for hydrogen generation. A facile strategy has been developed to fabricate highly active electrodes with hierarchical porous structures by using a two-step electrodeposition method, in which NiFe layered double hydroxide is grown in situ on a three-dimensional hierarchical Ni mesh (NiFe/Ni/Ni). The as-prepared NiFe/Ni/Ni electrodes demonstrate remarkable structural stability with high surface areas, effective gas transportation, and fast electron transfer. Benefiting from the unique structure, the self-supported NiFe/Ni/Ni electrodes exhibit overpotentials of 190 mV and 300 mV for the oxygen evolution reaction (OER) at current densities of 10 and 500 mA cm^-2 , respectively. Furthermore, the self-supported NiFe/Ni/Ni electrodes also exhibit high performance in the hydrogen evolution reaction (HER) and excellent stability at a current density of 500 mA cm^-2 for both OER and HER. Remarkably, using NiFe/Ni/Ni as both the cathode and anode for alkaline water electrolysis, a current density of 500 mA cm^-2 is attained at a cell voltage of 1.96 V. Additionally, the water electrolyzer demonstrates superior stability even at a large current density (500 mA cm^-2 ) when subjected to high temperatures.

Hierarchical Co–FeS2/CoS2 heterostructures as a superior bifunctional electrocatalyst

The traditional method of preparing hydrogen and oxygen as efficient clean energy sources mainly relies on the use of platinum, palladium, and other precious metals. However, the high cost and low abundance limit wide application of such metals. As such, one challenging issue is the development of low-cost and high-efficiency electrocatalysts for such purposes. In this study, we synthesized Co–FeS₂/CoS₂ heterostructures via a hydrothermal method for efficient hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Benefitting from their unique three-dimensional hierarchical nanostructures, Co-doped FeS₂, and CoS₂ formed heterostructures on Co–FeS₂ petals, which bestowed remarkable electrocatalytic properties upon Co–FeS₂/CoS₂ nanostructures. Co–FeS₂/CoS₂ effectively catalyzed the OER with an overpotential of 278 mV at a current density of 10 mA cm⁻² in 1 M KOH solution, and also is capable of driving a current density −10 mA cm⁻² at an overpotential of −103 mV in 0.5 M H₂SO₄ solution. The overpotential of the OER and HER only decreased by 5 mV and 3 mV after 1000 cycles. Our Co–FeS₂/CoS₂ materials may offer a promising alternative to noble metal-based electrocatalysts for water splitting.

Here we report a facile solvothermal synthesis of Co–FeS₂/CoS₂ heterostructures with remarkable electrocatalytic properties.