Water Splitting In Alkaline Electrolyte Research Articles

Surface reconstruction of NiCoP pre-catalysts for bifunctional water splitting in alkaline electrolyte

The emerging earth-abundant metal phosphides are regarded as promising bifunctional water splitting electrocatalysts. However, the real active sites in metal phosphides remain a debate. Herein, the hierarchical flower-like NiCoP microsphere is designed with the outstanding performance toward both hydrogen and oxygen evolution reaction (overpotentials of 238 and 47 mV for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) at 10 mA cm−2, respectively). The symmetrical overall water splitting devices based on NiCoP only require an ultralow voltage of 1.52 V to reach 10 mA cm−2, which is rarely reported. In-situ Raman and ex-situ TEM/XPS reveal that the surface reconstruction of designed NiCoP pre-catalysts transforms into metallic Ni(Co) for HER and Ni(Co)OOH for OER, respectively. The degradation process of HER during resting is revealed, suggesting the formation of high valence state Ni(Co)(OH)2 and blocking the active sites. We believe that the comprehensive understanding of the surface reconstruction of electrode is crucial in understanding the fundamental mechanism.

Enhancing hydrogen evolution reaction through modulating electronic structure of self-supported NiFe LDH

NiFe-layered double hydroxide (NiFe LDH), as an efficient oxygen evolution reaction (OER) electrocatalyst, has emerged as a promising electrocatalyst for catalyzing overall water splitting in alkaline electrolyte.

Iron–cobalt–nickel trimetal phosphides as high-performance electrocatalysts for overall water splitting

An iron–cobalt–nickel trimetal phosphide can work as bifunctional electrode materials for overall water splitting in alkaline electrolyte with good stability.

In situ assembly of metal-organic framework-derived N-doped carbon/Co/CoP catalysts on carbon paper for water splitting in alkaline electrolytes

High-performance and cost-effective catalysts for water splitting are key components of hydrogen-based energy technologies. Metal-organic framework (MOF)-derived metal phosphide composites have immense potential as highly active and stable electrocatalysts but suffer from the poor efficacy of available electrode assembly methods. In this study, an MOF-derived nitrogen-doped porous carbon/Co/CoP/carbon paper (NC/Co/CoP/CP) composite electrode was assembled by electrophoretic deposition and post-processing reactions. The binder-free electrode showed good catalytic activity, significantly higher than that of traditional electrodes.</a> The electrode required overpotentials of 208 and 350 mV to achieve a current density of 10 mA/cm2 for the hydrogen and oxygen evolution reactions, respectively.</a> This facile synthetic method provides a promising route for designing metal-doped and multi-metal phase MOF-derived composite electrodes for energy storage and conversion devices.

In-situ formed N doped bamboo-like carbon nanotube decorated with Fe–Ni–Cr nanoparticles as efficient electrocatalysts for overall water-splitting

It is of tremendous significance to develop effective bifunctional electrocatalysts for electrochemical water-splitting to generate sustainable hydrogen energy. Herein, a facile and scalable strategy is evolved to design N doped bamboo-like carbon nanotube decorated with tri-metal nanoparticles (Fe–Ni–Cr/NC) for overall water-splitting in alkaline electrolyte. Coupling effects between different metals and intimately contact with the carbon matrix endow the obtained nanomaterial possesses splendid catalytic activity and stability for cathodic HER, anodic OER and overall water-splitting in alkaline electrolyte. The obtained Fe–Ni–Cr/NC exhibits the best catalytic performance for HER (284 mV@10 mA cm−2) relative to Fe–Cr/NC (368 mV), Ni–Cr/NC (314 mV) and Fe–Ni/NC (324 mV). For OER, a small overpotential of 210 mV is needed to drive 10 mAcm−2 which is superior to IrO2 (330 mV). Thus, the interactions between different metals act as paramount effects on promoting the catalytic activities. Benefiting from the outstanding catalytic performances for both HER and OER, the designed Fe–Ni–Cr/NC possesses splendid catalytic activity for overall water-splitting with a small potential of 1.64 V to deliver 10 mA cm−2. Moreover, the obtained nanomaterial also owns remarkable long-term stability in the measured electrolyte.

A hierarchically porous and hydrophilic 3D nickel–iron/MXene electrode for accelerating oxygen and hydrogen evolution at high current densities

Electrocatalytic water-splitting is one of the most economical and clean way for high-purity hydrogen production utilizing renewable energy sources. Key issue to large-scale implementation of this technology is the lack of efficient electrocatalysts that can deliver large current density at low overpotential for oxygen and hydrogen evolution reactions (OER and HER). Herein, we report a strategy leveraging 3D MXene frame with high conductivity, highly hydrophilic properties and kinetics-favorable architecture as multi-functional structural scaffold for engineering water-splitting electrocatalysts yielding high current densities. The macroporous 3D MXene frame not only facilitates the mass/charge transport across the catalyst, but also accelerates the OER redox process of NiFe-LDHs and the Volmer step of HER by enhancing the water adsorption/activation on the catalyst. Commercially required high current density of 500 mA cm−2 can be achieved at low overpotentials for both OER (300 mV) and HER (205 mV) with good durability in 1.0 M KOH. Alkaline electrolyzer using this electrocatalytic electrode as both the anode and cathode exhibit low cell voltage for achieving high current density of 500 mA cm−2 with high Faradaic efficiency and excellent durability. Their performance outperforms the Pt/C–RuO2 couple and the state-of-the-art electrocatalysts for overall water-splitting in alkaline electrolyte.

Self-standing and efficient bifunctional electrocatalyst for overall water splitting under alkaline media enabled by Mo1-xCoxS2 nanosheets anchored on carbon fiber paper

Abstract The layered MoS2 nanostructures have been widely used in the electrochemical hydrogen evolution reaction (HER), but rarely applied in overall water splitting application for their ignorable oxygen evolution reaction (OER) activity. To address this issue, a novel self-standing and bifunctional electrocatalyst, consisting of Co-doped MoS2 nanosheets anchored on carbon fiber paper, has been prepared via hydrothermal method. Taking advantage of conductive substrate of carbon fiber paper, sufficient-exposed active edges of MoS2 sheets, and metallic character caused by Co-doping, our electrode exhibits high-efficient bifunctional activities for the overall water splitting in alkaline electrolyte (1 M KOH), which can produce a current density of 20 mA cm−2 at an overpotential of 197 mV for HER and 235 mV for OER.

Self-adaptive amorphous Co2P@Co2P/Co-polyoxometalate/nickel foam as an effective electrode for electrocatalytic water splitting in alkaline electrolyte

Noble-metal-free transition metal based phosphides (TMPs) display great potential as candidates to replace the state-of-the-art noble metal-based catalysts for electronic water splitting. In this study, amorphous Co2P was decorated on Co-polyoxometalate (POM) and conductive cobalt phosphide forming integrated Co2P@ Co2P/Co-POM/NF electrode, through in suit growth, low-temperature phosphating and electrocatalytic self-adaption pathway by the stripping of superficial Co-POM when subjected to persistent bubbles. The fantastic design simultaneously offers excellent electrical conductivity for fast electron transfer, a large surface area with numerous active edge sites and a conductive current collector facilitating mass transfer and gas release. The electrode showed high catalytic activity, requiring overpotential of 130 mV for HER to achieve a current density of 50 mA/cm2, 336 mV for OER to achieve a current density of 50 mA/cm2, affording a water-splitting current density of 10 mA/cm2 at a low cell voltage of 1.6 V. The results and facile synthesis method also offer an exciting avenue for the design of amorphous phase TMPs on a current collector with high specific area and excellent electrical conductivity for energy storage and conversion devices.

Electrochemical Performance of Borate‐Doped Nickel Sulfide: Enhancement of the Bifunctional Activity for Total Water Splitting

AbstractElectrolytic water splitting with solar electricity is one of the few technologies which can produce hydrogen with nearly zero carbon emission. The viability of the technology depends on the availability of low‐cost alternatives to the platinum group metals (PGMs); which are the best known electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER). In this study, borate doping of nickel sulfide was found to yield catalysts which are effective for total water electrolysis. For the borate‐doped nickel sulfides ((BO3)x−Ni3S4, x=0, 0.57, 0.78 and 1.08), the strong affinity of borate for hydroxyl groups facilitates the dissociation of adsorbed water molecules to oxygen. Consequently, the borate‐doped nickel sulfide catalyst with the best performance in this study, (BO3)1.08−Ni3S4, requires only a small overpotential of 306 mV to support a current density of 10 mA cm−2 in OER. This, together with a small Tafel slope of 36.5 mV decade−1 and a stable extended operation; places (BO3)1.08−Ni3S4 among the top non‐PGM OER electrocatalysts reported to date. At the same time (BO3)1.08−Ni3S4 also shows good HER activity and stability for it to be used as a standalone catalyst for efficient total water splitting in alkaline electrolyte (1.69 V at 10 mA cm−2).

Iron doped cobalt phosphide ultrathin nanosheets on nickel foam for overall water splitting

Iron doped cobalt phosphide ultrathin nanosheets on nickel foam are used as a bifunctional electrocatalyst for overall water splitting in alkaline electrolyte.

Systematic design of superaerophobic nanotube-array electrode comprised of transition-metal sulfides for overall water splitting

Great attention has been focused on the design of electrocatalysts to enable electrochemical water splitting—a technology that allows energy derived from renewable resources to be stored in readily accessible and non-polluting chemical fuels. Herein we report a bifunctional nanotube-array electrode for water splitting in alkaline electrolyte. The electrode requires the overpotentials of 58 mV and 184 mV for hydrogen and oxygen evolution reactions respectively, meanwhile maintaining remarkable long-term durability. The prominent performance is due to the systematic optimization of chemical composition and geometric structure principally—that is, abundant electrocatalytic active sites, excellent conductivity of metallic 1T’ MoS2, synergistic effects among iron, cobalt, nickel ions, and the superaerophobicity of electrode surface for fast mass transfer. The electrode is also demonstrated to function as anode and cathode, simultaneously, delivering 10 mA cm−2 at a cell voltage of 1.429 V. Our results demonstrate substantial improvement in the design of high-efficiency electrodes for water electrolysis.

In-Situ Formed Hydroxide Accelerating Water Dissociation Kinetics on Co3N for Hydrogen Production in Alkaline Solution

Sluggish water dissociation kinetics on nonprecious metal electrocatalysts limits the development of economical hydrogen production from water-alkali electrolyzers. Here, using Co3N electrocatalyst as a prototype, we find that during water splitting in alkaline electrolyte a cobalt-containing hydroxide formed on the surface of Co3N, which greatly decreased the activation energy of water dissociation (Volmer step, a main rate-determining step for water splitting in alkaline electrolytes). Combining the cobalt ion poisoning test and theoretical calculations, the efficient hydrogen production on Co3N electrocatalysts would benefit from favorable water dissociation on in-situ formed cobalt-containing hydroxide and low hydrogen production barrier on the nitrogen sites of Co3N. As a result, the Co3N catalyst exhibits a low water-splitting activation energy (26.57 kJ mol-1) that approaches the value of platinum electrodes (11.69 kJ mol-1). Our findings offer new insight into understanding the catalytic mechanism of nitride electrocatalysts, thus contributing to the development of economical hydrogen production in alkaline electrolytes.

Dual-Functional Starfish-like P-Doped Co-Ni-S Nanosheets Supported on Nickel Foams with Enhanced Electrochemical Performance and Excellent Stability for Overall Water Splitting.

Dual-functional electrocatalysts have recently been reported to improve the conversion and storage of energy generated from overall water splitting in alkaline electrolytes. Herein, for the first time, a shape-controlled synthesis of starfish-like Co-Ni-S nanosheets on three-dimensional (3D) hierarchically porous nickel foams (Co-Ni-S/NF) via a one-step hydrothermal method was developed. The influence of reaction time on the nanosheet structure and properties was intensively studied. After 11 h reaction, the Co-Ni-S/NF-11 sample displays the most regular structure of nanosheets and the most outstanding electrochemical properties. As to water splitting, hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) required overpotentials of 284.3 and 296 mV, respectively, to provide a current density of 100 mA cm-2. The marvelous electrochemical performance can be attributed to the conductive networks of 3D layered porous nickel skeletons that are highly interconnected, which provided a large specific area and highly active sites. To further enhance the electrochemical performances of the electrocatalyst, the influence of the doping of the P element was also studied. The results proved that the P-doped Co-Ni-S/NF maintains the starfish structure and demonstrates outstanding properties, providing a current density of 100 mA cm-2 with only 187.4 and 292.2 mV overpotentials for HER and OER, respectively. It exhibited far more excellent properties than reported dual-functional electrocatalysts. Additionally, when used as an overall water-splitting catalyst, P-Co-Ni-S/NF can provide a 10 mA cm-2 current density at a given cell voltage of 1.60 V in 1 M KOH, which is competitive to the best-known electrocatalysts, with high long-term stability.

Cobalt-based nanosheet arrays as efficient electrocatalysts for overall water splitting

Herein we report a simple electrochemical approach to synthesize cobalt-based nanosheet arrays as efficient and robust electrocatalysts for overall water splitting in alkaline electrolytes.

Enhancing electrocatalytic activity of bifunctional Ni3Se2 for overall water splitting through etching-induced surface nanostructuring

Abstract

Nickel-coated silicon photocathode for water splitting in alkaline electrolytes

Photoelectrochemical (PEC) water splitting is a promising approach to harvest and store solar energy [1]. Silicon has been widely investigated for PEC photoelectrodes due to its suitable band gap (1.12 eV) matching the solar spectrum [2]. Here we investigate employing nickel both as a catalyst and protecting layer of a p-type silicon photocathode for photoelectrochemical hydrogen evolution in basic electrolytes for the first time. The silicon photocathode was made by depositing 15 nm Ti on a p-type silicon wafer followed by 5 nm Ni. The photocathode afforded an onset potential of ∼0.3 V vs. the reversible hydrogen electrode (RHE) in alkaline solution (1 M KOH). The stability of the Ni/Ti/p-Si photocathode showed a 100 mV decay over 12 h in KOH, but the stability was significantly improved when the photocathode was operated in potassium borate buffer solution (pH ≈ 9.5). The electrode surface was found to remain intact after 12 h of continuous operation at a constant current density of 10 mA/cm2 in potassium borate buffer, suggesting that Ni affords good protection of Si based photocathodes in borate buffers.