Oxygen evolution reaction (OER) has a high overpotential, which can significantly reduce the energy efficiency in water decomposition. Using urea oxidation reaction (UOR) to replace OER has been a ...feasible and energy-saving approach because of its lower electrode potential. Furthermore, UOR is also an important process in wastewater treatment. This paper successfully synthesizes a high-performance bifunctional catalyst for urea electrolysis. The catalyst is nickel nitride bead-like nanospheres array supported on Ni foam (Ni
N/NF). Several characterization methods are used to analyze the catalyst's morphology, structure, and composition as well as catalytic activity/stability, including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and electrochemical methods (cyclic voltammetry, linear sweep voltammetry, electrochemical impedance spectroscopy, and CAM). A concurrent two-electrode electrolyzer (Ni
N/NF∥Ni
N/NF) is constructed and used to validate the catalyst performance, and the results show that the cell achieves 100 mA·cm
at 1.42 V, while the cell voltage of Pt/C∥IrO
is 1.60 V, indicating that the Ni
N/NF catalyst is superior to precious metals.
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•Overpotential fluctuations due to bubbles are studied in the absence of hyperpolarization.•Instantaneous gas evolution efficiency of bubbles increases with increasing current.•Bubbles lower ...concentration overpotential and this effect increases with increasing current and bubble radius.•Bubbles increase ohmic overpotential especially after they outgrow the electrode.
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The presence of bubbles in gas-evolving electrolytic processes can heavily alter the mass transport of gaseous products and can induce severe overpotential penalties at the electrode through the action of bubble coverage (hyperpolarization) and electrolyte constriction (Ohmic shielding). However, bubble formation can also alleviate the overpotential by lowering the concentration of dissolved gas in the vicinity of the electrode. In this study, we investigate the latter by considering the growth of successive hydrogen bubbles driven by a constant current in alkaline-water electrolysis and their impact on the half-cell potential in the absence of hyperpolarization. The bubbles nucleate on a hydrophobic cavity surrounded by a ring microelectrode which remains free of bubble coverage. The dynamics of bubble growth does not adhere to one particular scaling law in time, but undergoes a smooth transition from pressure-driven towards supply-limited growth. The contributions of the different bubble-induced phenomena leading to the rich behaviour of the periodic fluctuations of the overpotential are identified throughout the different stages of the bubble lifetime, and the influence of bubble size and applied current on the concentration and Ohmic overpotential components is quantified. We find that the efficiency of gas absorption, and hence the concentration-lowering effect, increases with increasing bubble size and also with increasing current. However, the concentration-lowering effect is always eventually countered and overcome by the effect of Ohmic shielding as the bubble size outgrows and eclipses the electrode ring beneath.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Nonprecious transition metal (oxy)hydroxides play a vital role in accelerating the kinetics of sluggish oxygen evolution reaction (OER). The fast electron transfer from the electrocatalyst material ...surface to the electrode is key to obtaining improved OER activity in terms of improved reaction kinetics and reduced overpotential. Therefore, it is highly desirable to design electrocatalysts with efficient electron transport properties. Here, an approach of modulation of the morphology of Iron (oxy)hydroxide through the incorporation of Cr is used to obtain high electrocatalytic activity. The incorporation of Cr resulted in the modified morphology of Iron (oxy)hydroxide with the formation of a porous pit-like structure which offers large reactive sites to effectively adsorb the reactants and allow an efficient electron transfer pathway from electrocatalyst to circuit through Ni foam electrode. A 50 % Cr incorporated electrocatalyst (Fe5.0Cr5.0 (oxy)hydroxide) exhibits excellent OER activity with an overpotential of 237 mV and 297 mV at current densities of 10 and 100 mA cm─2, respectively owing to fast electron transport from electrocatalyst to substrate due to formation of porous pit-like structure. Furthermore, Fe5.0Cr5.0 electrocatalyst shows high durability of over 100 h at 10 mA cm─2. The enhanced OER activity is attributed to the effect of Cr incorporation and morphology modulation which helps to modulate the electronic structure as well as electrocatalytic active sites of Fe (oxy)hydroxide. The systematic incorporation and modulation of morphology pave the way for designing future electrocatalysts for various electrochemical activities.
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•Cr-modified Fe(oxy)hydroxide boosts electrocatalytic activity effectively.•Porous structure enhances reactant adsorption for improved performance.•Efficient electron transfer via Ni foam enriches overall catalyst efficacy.•Fe5.0Cr5.0 (oxy)hydroxide excels in OER with low overpotentials.•Impressive 100-hour durability at 10 mA/cm² showcases catalyst robustness.
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Reducing the gap between the electrodes and diaphragm to zero is an often adopted strategy to reduce the ohmic drop in alkaline water electrolyzers for hydrogen production. We provide a thorough ...account of the current–voltage relationship in such a zero-gap configuration over a wide range of electrolyte concentrations and current densities. Included are voltage components that are not often experimentally quantified like those due to bubbles, hydroxide depletion, and dissolved hydrogen and oxygen. As is commonly found for zero-gap configurations, the ohmic resistance was substantially larger than that of the separator. We find that this is because the relatively flat electrode area facing the diaphragm was not active, likely due to separator pore blockage by gas, the electrode itself, and or solid deposits. Over an e-folding time-scale of ten seconds, an additional ohmic drop was found to arise, likely due to gas bubbles in the electrode holes. For electrolyte concentrations below 0.5 M, an overpotential was observed, associated with local depletion of hydroxide at the anode. Finally, a high supersaturation of hydrogen and oxygen was found to significantly increase the equilibrium potential at elevated current densities. Most of these voltage losses are shown to be easily avoidable by introducing a small 0.2 mm gap, greatly improving the performance compared to zero-gap.
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•Bubble and concentration overpotential quantification for a zero-gap electrolyzer.•An inactive electrode front explains the anomalously large separator resistance.•An additional ohmic drop arises transiently, likely due to gas bubbles.•Introducing a 0.2 mm gap strongly reduces the resistance.•Local hydroxide depletion gives large losses at low electrolyte concentrations.
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Oxygen evolution reaction (OER) electrocatalysts are confronted with challenges such as sluggish kinetics, low conductivity, and instability, restricting the development of water splitting. In this ...study, we report an efficient Co(3+)-rich cobalt selenide (Co0.85Se) nanoparticles coated with carbon shell as OER electrocatalyst, which are derived from zeolitic imidazolate framework (ZIF-67) precursor. It is proposed that the organic ligands in the ZIF-67 can effectively enrich and stabilize the Co(3+) ions in the inorganic-organic frameworks and subsequent carbon-coated nanoparticles. In alkaline media, the catalyst exhibits excellent OER performances, which are attributed to its abundant active sites, high conductivity, and superior kinetics.
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This review categorizes different types of electrocatalysts for water splitting application and summarizes the strategies for enhancing bifunctional performances as well as the remaining challenges ...for future hydrogen economy.
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•Different types of electrocatalysts are categorized for water splitting application.•Strategies for enhancing bifunctional performances are highlighted.•Overall water splitting properties of catalysts are compared and summarized.•Remaining challenges are clearly pointed out for future hydrogen economy.
Water electrolysis plays a crucial role among the strategies for hydrogen generation to replace the conventional fossil fuels. Many efforts have been devoted to developing efficient electrocatalysts for the water electrolysis process. The exploration of suitable catalytic materials with low overpotential, fast kinetic, and good electrochemical stability is actively pursued for both hydrogen and oxygen evolution reaction (HER/OER) as well as overall water splitting. Today’s hydrogen economy keeps on being driven by the characteristics of electrocatalytic materials. In this review, recent advancements achieved in electrocatalysts of water electrolysis are overviewed together with some strategies for performance improvements, such as nanoarchitecturing, heteroatomic doping, surface modulation and interface engineering. Furthermore, some of the latest achievements in the fabrication of electrode materials as practical demonstration on their viability are also discussed. With better understanding on these topics, the rationales behind their enhanced electrochemical performances are revealed and explained. Last but not least, the existing challenges and opportunities are briefly proposed for future upgradation of the water splitting performance.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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The water oxidation process, which comprises the oxygen evolution reaction (OER), is a critical catalytic mechanism for sustainable technologies like water electrolysis and fuel ...cells. Herein, we develop a unique metal–organic framework aided vanadium pentoxide nanorods (MOF-V2O5 NRs-500) that can be used as an OER electrocatalyst under alkaline solutions. The crystal structure, surface chemical state, and porosity of MOF-V2O5 NRs-500 can be altered by annealing in an oxygen atmosphere. The resultant MOF-V2O5 NRs-500 demonstrate high catalytic activity against OER in basic conditions, with a low overpotential of 300 mV at a derived current density of 50 mA cm−2, and extraordinary durability of more than 50 h. Superior electrochemical performance might be attributed to the high exposure level of active sites emanating from porous MOF-V2O5 NRs-500. Furthermore, the porous MOF-V2O5 NRs-500 skeleton may provide homogenous mass transport channels as well as quick electron transfer.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Lithium-oxygen battery has high energy density which is considered as promising candidate for next-generation energy storage system. One of the major challenges for Li–O2 battery is exploring ...efficient catalysts for the decomposition of Li2O2 and by-products. In this work, a robust cathode employing RuO2·nH2O clusters anchored on the carbon nanofibers (RNCs@CNFs) is fabricated for Li–O2 battery. RNCs demonstrate an excellent oxidation activity towards both Li2O2 and Li2CO3 during the oxygen evolution reaction (OER). The unique structure of RuO2·nH2O clusters also alleviate the deactivation caused by the coverage of active sites. As a result, the as-built battery exhibits a high specific capacity, a superior rate capability and an excellent cycling stability with low overpotentials. After 200 cycles, new Li anode is replaced and the battery continues 100 cycles without attenuation at a limited capacity of 1000 mAh g−1 and a current of 200 mA g−1. These results provide necessary information for the development of efficient cathode catalysts for the decomposition of Li2O2 and Li2CO3 in Li-air batteries.
•A robust cathode employing RNCs@CNFs is fabricated.•RNCs@CNFs accelerate the decomposition of both Li2O2 and Li2CO3.•The unique structure of RNCs alleviates the deactivation of the carbon-based cathode.•The cathode exhibits extremely long cycle life.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Increasing demand for finding eco-friendly and everlasting energy sources is now totally depending on fuel cell technology. Though it is an eco-friendly way of producing energy for the urgent ...requirements, it needs to be improved to make it cheaper and more eco-friendly. Although there are several types of fuel cells, the hydrogen (H2) and oxygen (O2) fuel cell is the one with zero carbon emission and water as the only byproduct. However, supplying fuels in the purest form (at least the H2) is essential to ensure higher life cycles and less decay in cell efficiency. The current large-scale H2 production is largely dependent on steam reforming of fossil fuels, which generates CO2 along with H2 and the source of which is going to be depleted. As an alternate, electrolysis of water has been given greater attention than the steam reforming. The reasons are as follows: the very high purity of the H2 produced, the abundant source, no need for high-temperature, high-pressure reactors, and so on. In earlier days, noble metals such as Pt (cathode) and Ir and Ru (anode) were used for this purpose. However, there are problems in employing these metals, as they are noble and expensive. In this review, we elaborate how the group VIII 3d metal sulfide, selenide, and phosphide nanomaterials have arisen as abundant and cheaper electrode materials (catalysts) beyond the oxides and hydroxides of the same. We also highlight the evaluation perspective of such electrocatalysts toward water electrolysis in detail.
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Rechargeable aqueous zinc-iodine batteries have received extensive attention due to their inherent advantages such as low cost, flame retardancy and safety. To address the safety concern associated ...with Zn dendrites, tin functional layer is introduced to the Zn surface via a spontaneous galvanic replacement reaction. This provides rapid deposition kinetics, thereby achieving the uniform Zn plating/stripping with a low overpotential (13.9 mV) and good stability for over 900 h. Importantly, the coupling of the advanced Zn anode with iodine in Zn-I2 battery exhibits a high specific capacity of 196.4 mAh·g−1 with high capacity retention (90.7%). This work provides a reliable strategy to regulate the reversible redox of zinc for advanced rechargeable batteries.
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