Mixed Transition Metal Carbonate Hydroxide‐Based Nanostructured Electrocatalysts for Alkaline Oxygen Evolution: Status and Perspectives

Abstract

To date, conventional fossil fuels have been considered the main energy source for modern civilization. [1] The nonrenewable nature and continuous depletion of fossil fuels and the increasing CO 2 emission levels necessitate the development of cost-effective renewable energy conversion/storage systems. [2][3][4][5] In this context, hydrogen, as a fuel, is considered an important alternative to many conventional energy resources owing to its several advantages, such as facile energy storage/carrier, high energy density, and zero-emission upon combustion. [6][7][8] Hydrogen has applications in heat generation, [9] refining processes in industry, [10] and provides electricity in stationary and transport/ vehicle. [11] Hydrogen can be manufactured using a variety of methods, such as hightemperature steam reforming, water electrolysis, solar water splitting-thermolysis, and biomass conversion. [12] Among these methods, steam reforming is the preferred method; it fulfills %96% of global hydrogen demand. [13,14] However, this process requires high temperatures (700-1100 °C) and fossil fuels/natural hydrocarbons, and it is accompanied by greenhouse gas (CO 2 ) emissions. [15][16][17] Among various hydrogen production technologies, water electrolysis can be considered a major contributor to the production of ultrapure hydrogen (>99.9%); moreover, water electrolysis is environmentally benign. In addition, the electrolysis of water in alkaline media is a highly cost-effective, sustainable, and industrially viable method for hydrogen production. [18] However, efficient hydrogen production through water electrolysis is limited by the high overpotential and sluggish kinetics of the anodic oxygen evolution reaction (OER) and the cathodic hydrogen evolution reaction (HER). [11] The OER involves four-electron transfer pathways under acidic and alkaline conditions. Further, OER is associated with many other energy conversion and storage processes/devices, such as solar fuel production [2] and metal-air batteries. [19] The OER is a four-electron transfer process and has a relatively higher overpotential than the HER and a complex reaction mechanism; hence, OER can be considered the rate-determining step (RDS) for hydrogen production through water electrolysis. [20] Furthermore, the OER has unusually low rate constants and high

Experimental and Theoretical Insights of Anion Regulation in MOF-Derived Ni–Co-Based Nanosheets for Supercapacitors and Anion Exchange Membrane Water Electrolyzers

“…In recent times, research on the advancement of sustainable and eco-friendly energy storage/conversion technologies has attracted considerable attention from the scientific community to surmount the rising energy demands worldwide. − Among the different preeminent energy storage cells, supercapacitors (SCs) have gained extensive interest owing to their intrinsic safety, rapid charging/discharging, high power density, durability, and high efficiency. − However, the relatively lower specific energy of SCs compared to that of conventional secondary batteries has restricted their commercial application. − Assembling asymmetric SCs (ASCs) using battery-like Faradaic positive materials and nanoporous carbon-related negative materials with superior capacity and a large working voltage window could produce an exalted energy density. Apart from energy storage, the production of high-purity and renewable hydrogen fuel using electrochemical water-splitting (EWS) technology (energy conversion device) is considered an indispensable future energy resource. ,− The EWS process includes two core half-cell reactions: hydrogen and oxygen evolution reactions (HER and OER, respectively) at the cathode and anode sides, respectively. , The OER process is more crucial and requires a higher overpotential than the HER because of its four-electron-transfer process associated with sluggish reaction kinetics. The state-of-the-art precious iridium (Ir) and ruthenium (Ru)-based transition metal oxides (TMOs) are employed as suitable electrocatalysts for accelerating the OER process .…”

“…2,11−13 The EWS process includes two core half-cell reactions: hydrogen and oxygen evolution reactions (HER and OER, respectively) at the cathode and anode sides, respectively. 14,15 The OER process is more crucial and requires a higher overpotential than the HER because of its four-electron-transfer process associated with sluggish reaction kinetics. The state-of-the-art precious iridium (Ir) and ruthenium (Ru)-based transition metal oxides (TMOs) are employed as suitable electrocatalysts for accelerating the OER process.…”

Morphology-controlled synthesis of a NiCo-carbonate layered double hydroxide as an electrode material for solid-state asymmetric supercapacitors

“…21,22 Bimetallic carbonate hydroxide (CH) is an emerging material that has multiple metal oxidation states and redox reaction activity. It has received significant attention as an electrode material for the oxygen evolution reaction 23 and for supercapacitor applications. 24 The inorganic lamellar structure of bimetallic hydroxide anions has a typical formula of [M 2Àx 2+ M x 3+ (OH) 4Àn A nÀ ]ÁmH 2 O, where M 2+ are bivalent, M 3+ are trivalent metal cations and A nÀ are anions (e.g., CO 3 2À , NO 3 2À , Br À ).…”

Recent Advances of Transition Metal Basic Salts for Electrocatalytic Oxygen Evolution Reaction and Overall Water Electrolysis

“…In brief, it is no doubt that TM basic salts are one of the most promising pre-catalysts for OER, however, there has not been a comprehensive review for TM basic salts except for two reviews on TM carbonate hydroxides [29,99].…”