Water Splitting In Alkaline Electrolyte Research Articles

Electronic transfer and structural reconstruction in porous NF/FeNiP-CoP@NC heterostructure for robust overall water splitting in alkaline electrolytes

Multimetal phosphides derived from metal-organic frameworks (MOFs) have garnered significant interest owing to their distinct electronic configurations and abundant active sites. However, developing robust and efficient catalysts based on metal phosphides for overall water splitting (OWS) remains challenging. Herein, we present an approach for synthesizing a self-supporting hollow porous cubic FeNiP-CoP@NC catalyst on a nickel foam (NF) substrate. Through ion exchange, the reconstruction chemistry transforms the FeNi-MOF nanospheres into intricate hollow porous FeNi-MOF-Co nanocubes. After phosphorization, numerous N, P co-doped carbon-coated FeNiP-CoP nanoparticles were tightly embedded within a two-dimensional (2D) carbon matrix. The NF/FeNiP-CoP@NC heterostructure retained a porous configuration, numerous heterogeneous interfaces, distinct defects, and a rich composition of active sites. Moreover, incorporating Co and the resulting structural evolution facilitated the electron transfer in FeNiP-CoP@NC, enhancing the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) processes. Consequently, the NF/FeNiP-CoP@NC catalyst demonstrated very low overpotentials of 78 mV for OER and 254 mV for HER in an alkaline medium. It also exhibited excellent long-term stability at various potentials (@10 mA cm−2, @20 mA cm−2, and @50 mA cm−2). As an overall water splitting cell, it required only 1.478 V to drive a current density of 50 mA cm−2 and demonstrated long-term stability. Density functional theory (DFT) calculations revealed a synergistic effect between multimetal phosphides, enhancing the intrinsic OER and HER activities of FeNiP-CoP@NC. This work not only elucidates the role of heteroatom induction in structural reconstruction but also highlights the importance of electronic structure modulation.

Dynamically assisted electrodeposition by hydrogen bubbles on carbonized wood: A NiFeCo nanoflower electrocatalyst for efficient hydrogen evolution

The development of cost-effective, simple, and highly active catalysts for electrochemical water splitting in alkaline electrolytes to produce renewable source H2 is critical to solve the environmental pollution and energy crisis. In this study, a series of nanoflower-like NiFeCo/CW catalytic electrodes were prepared by a facile one-step dynamic hydrogen bubble template (DHBT) method for electrodeposition on carbonized wood (CW), which have excellent HER performance. By reasonably investigating the effects of H+ concentration and time, a catalyst with ideal deposition results was obtained. In 1 M KOH solution, the prepared NiFeCo/CW-450 catalyst exhibits a small overpotential of 37 mV to achieve a current density of 10 mA cm−2, and still possess a satisfactory low overpotential when a larger current density is reached (η400 = 238 mV, η1000 = 298 mV). Furthermore, NiFeCo/CW can keep structure and catalytic performance stable after long-term test. The remarkable HER performance results from the unique nanoflower electrode structure that is uniformly dispersed on CW to fully expose the active site. As a result, this work will provide new inspiration and strategy for the preparation of novel simple, inexpensive and efficient electrocatalytic hydrogen evolution electrodes using earth-abundant resources.

Bimetallic and phosphorus-decorated cobalt molybdate nanosheets as highly active bifunctional electrocatalysts for enhanced overall water splitting

It is very vital to exploit efficient electrocatalysts for water splitting. Herein, we design and fabricate one kind of bimetallic and phosphorus-doped CoMoO4 (P–CoMoO4) nanosheet product with coarse surface and porous structure. The P–CoMoO4 nanosheets possess rectangular architecture with the length and width of ∼2 μm and 500 nm. It is worth noting that the synthetic P–CoMoO4 catalyst displays bifunctional activity for overall water splitting in alkaline electrolyte. The overpotentials are merely 300 and 70.2 mV for OER and HER at 10 mA cm−2, respectively. The water splitting voltage of P–CoMoO4 couple is 1.48 V at 10 mA cm−2, and this couple presents reliably long-term stability for 24 h. This research indicates the important significance of bimetallic and phosphorus-decorated oxides in water electrolysis field.

Core-shell structured Co(OH)F@FeOOH enables highly efficient overall water splitting in alkaline electrolyte

Constructing a low-cost, high activity and stable electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) via overall water splitting is of great significance, but remains a big challenge. In this work, vertically aligned core-shell Co(OH)F@FeOOH nanorod arrays (NRs) on Ni foam were constructed via hydrothermal and chemical deposition methods. Due to the synergistic effects and electron interaction at the interface between Co(OH)F and FeOOH, the synthesized core-shell Co(OH)F@FeOOH heterostructure exhibits remarkable OER and HER catalytic activity in 1 M KOH solution, presenting low overpotentials of approximately 205 mV and 137 mV at a current density of 10 mA cm−2, and low Tafel slopes of approximately 48 mV dec−1 and 86 mV dec−1, for OER and HER, respectively. Moreover, the synthesized Co(OH)F@FeOOH serves as a bifunctional electrocatalyst for overall water splitting and it only needs 1.55 V to drive the electrolysis cell yielding 10 mA cm−2 which is much lower than that of 1.68 V for IrO2||Pt/C and showing excellent stability for 37 h. The prepared Co(OH)F@FeOOH catalyst has been successfully used in solar cell-driven water electrolysis, demonstrating its great potential for cost-effective electrochemical hydrogen production.

Pulsed laser ablation production of Ni/NiO nano electrocatalysts for oxygen evolution reaction

Efficient and sustainable materials are requested to overcome the actual major issues related to green energy production. Ni/NiO nanoparticles (NPs, 2–4 nm in size) produced by Pulsed Laser Ablation in Liquid (PLAL) are reported as highly efficient and stable electrocatalysts for oxygen evolution reaction (OER) in water splitting applications. Ni/NiO NPs dispersions are obtained by ablating a Ni target immersed in deionized water with an Nd:YAG nanosecond pulsed laser. NPs size and density were driven by laser energy fluence (ranging from 8 to 10 J cm−2) and shown to have an impact on OER performance. Ni/NiO NPs were characterized by scanning and transmission electron microscopy, x-ray diffraction, photoemission spectroscopy, and Rutherford back-scattering spectrometry. By drop-casting onto graphene paper, anode electrodes were fabricated for electrochemical water splitting in alkaline electrolytes. The extrinsic and intrinsic catalytic performances for OER have been quantified, achieving an overpotential of 308 mV (at a current density of 10 mA cm−2) and unprecedented mass activity of more than 16 A mg−1, using NPs synthesized with the highest and lowest laser energy fluence, respectively. The impact of NPs’ size and density on OER performances has been clarified, opening the way for PLAL synthesis as a promising technique for highly efficient nano-electrocatalysts production.

Enhanced alkaline water splitting on cobalt phosphide sites by 4d metal (Rh)-doping method

The construction of effective water-splitting electrocatalysts in alkaline conditions is challenging due to lower water dissociation efficiency than in acidic conditions. In this study, we investigated the effect of doping 4d and 5d metals into the 3d metal active site of cobalt phosphide (CoxP) on the water-splitting reaction. Introducing Ru slightly improved hydrogen evolution efficiency, but Rh doping significantly enhanced the catalytic parameters with an overpotential of 0.03 V at 10 mA/cm2. Rh regulated the electronic structure of CoxP to improve proton reduction. The Rh-CoxP electrode showed a comparable catalytic efficiency to that of a Pt/C standard. Ir doping slightly improved catalytic reactivity, but not as much as Rh. Our results showed that doping 4d metal from the same group as Co maximizes the doping effect during hydrogen evolution. A lab-scale water electrolyzer built with Rh-CoxP successfully demonstrated catalytic water splitting in alkaline electrolyte.

A hierarchical cactus-like nanostructure as a bifunctional catalyst for overall water splitting

In this study, a hierarchical cactus-like nanostructure with cobalt doped iron disulfide (Co-FeS2) needle nanowires as trunks and nickel-iron layered double hydroxide (NiFe-LDH) nanosheets as branches was constructed as a self-supporting electrode for overall water splitting in alkaline electrolytes. A low electron density NiFe-LDH derived from the strong electronic interaction between sulfides and NiFe-LDH is remarkably effective in facilitating the adsorption of H2O and OH−, while the presence of Co atoms in FeS2 facilitates the hydrogen adsorption. Such a synergetic effect improved the HER performance in alkaline electrolytes significantly. In terms of the OER process, the Fe/Co oxyhydroxides produced from in situ phase transition from Co-FeS2 in conjunction with NiFe-LDH endow the electrode with excellent OER activity. Furthermore, the Co-FeS2 needle nanowires with metal-like conductivity allow for rapid electron transfer during electrochemical processes, and the hierarchical structure exposes substantial active sites and facilitates electrolyte penetration. In alkaline media, the electrode demonstrated outstanding HER and OER catalytic activity, requiring small overpotentials of 131 mV and 220 mV to reach current densities of 10 mA cm−2 and 20 mA cm−2, respectively. Moreover, it only needed 1.58 V to drive 10 mA cm−2 when utilized simultaneously as both cathode and anode for overall water splitting.

Multifunctional Amorphous Co Phosphosulfide-Coated Fe-Co Carbonate Hydroxide for Highly Efficient Overall Water Splitting

Non-noble metal electrocatalysts current represent an appealing alternative to noble metal electrocatalysts for water oxidation reaction in alkaline conditions. However, the poor water reduction reaction activities limit their performance in driving overall water splitting in alkaline electrolytes. Here, we report the preparation of bifunctional amorphous Co phosphosulfide-doped Fe-Co carbonate hydroxide on the surface of Ni foam (Co-S-P/Fe1Co1COH/NF) through hydrothermal and electrochemical techniques. The efficient full water oxidation and reduction properties of the Co-S-P/Fe1Co1COH/NF were verified in pH = 14 medium. The results proved that a phosphorus and sulfur co-depositing catalyst could exhibit excellent anodic oxidation and cathodic reduction activity for full water splitting. Furthermore, the optimal electrocatalyst can afford a current density of 10 mA cm−2 at an overpotential of only 73 mV for hydrogen evolution from water reduction and 50 mA cm−2 at 160 mV for oxygen evolution from water oxidation in 1.0 M KOH solution, showing better activities than most non-noble metal materials. The improved electrocatalytic activities could be attributed to the increased number of active sites and the synergetic cooperation in the prepared material. Additionally, the Co-S-P/Fe1Co1COH/NF catalyst as both cathode and anode only needs a voltage of 1.5 V to achieve 10 mA cm−2 in 1 M KOH solution for full water splitting, which lays a good foundation for full water splitting in practical applications.

A new route for the recycling of spent lithium-ion batteries towards advanced energy storage, conversion, and harvesting systems

A new, sustainable, recycling technology is developed for the first time by reusing all the components of spent LIBs (anode, cathode, separator, and current collectors) towards energy storage, conversion, and harvesting applications, considering the environmental concerns and valuable resources. The graphite anode and metallic aluminium cases are effectively recycled to produce two-dimensional graphene sheets that are reutilized for 3.0 V supercapacitors exhibit a high energy density of 31.9 Wh kg–1 with long cycle life. The spent cathode is regenerated as Ni–Mn–Co–oxide and employed as a novel bifunctional electrocatalyst for overall water splitting in alkaline electrolytes, which requires a low voltage of 1.58 V to achieve a current density of 10 mA cm−2. The metallic current collectors and polymeric separator are reused to construct a triboelectric nanogenerator, produces a maximum voltage of ~40 V and a current of ~160 nA with a peak power of 3 μW. Hence, this study provides a feasible strategy of recycling all the components from spent LIBs to develop next-generation energy storage, conversion, and harvesting devices.

Surface reconstruction of phosphorus-doped cobalt molybdate microarrays in electrochemical water splitting

It is highly desired but still challenging to develop highly efficient catalysts for electrochemical water splitting. Herein, we report the fabrication of phosphorus-doped monoclinic β-CoMoO4 (P-CoMoO4) on nickel foam as a high-efficiency and bifunctional electrocatalyst for overall water splitting in alkaline electrolyte. Surface reconstruction of P-CoMoO4 is witnessed and carefully investigated, which is converted into Co(OH)2-CoMoO4/P-CoMoO4 during the hydrogen evolution reaction (HER) process, and into CoOOH/P-CoMoO4 during the oxygen evolution reaction (OER) process. Notably, the reconstructed catalyst exhibits ultralow overpotentials of 44 mV to achieve a current density of 10 mA cm−2 for HER, and 260 mV to deliver a current density of 20 mA cm−2 for OER. Meanwhile, it only needs a small cell voltage of 1.54 V at 10 mA cm−2 for robust water splitting with outstanding long-term durability over 72 h at 50 mA cm−2. This study reveals the significance of surface reconstruction of transition metal oxides for highly efficient water electrolysis.

An Efficient Electrocatalyst Based on Vertically Aligned Heteroatom(B/N/P/O/S)‐Doped Graphene Array Integrated with FeCoNiP Nanoparticles for Overall Water Splitting

AbstractIron group metal phosphides (IMPs) are one of the most promising substitutes for non‐noble electrocatalysts in overall water splitting. In this work, an electrocatalyst system consisting of different vertically aligned heteroatom‐doped graphene arrays (X‐rGO, X = N, P, B, O, S) integrated with FeCoNiP nanoparticles (FeCoNiP@X‐rGO, X = N, P, B, O, S) is prepared for overall water splitting. The unique vertical structure and the synergistic effect between the P in P‐rGO and the P in FeCoNiP leads to the excellent electrocatalytic performance of FeCoNiP@P‐rGO by exhibiting low overpotentials (121 and 216 mV) at a current density of 10 mA cm−2 for hydrogen evolution reaction in 1 m KOH and 0.5 m H2SO4, respectively. As well as a low overpotential (354 mV) at a current density of 10 mA cm−2 for the oxygen evolution reaction in 1.0 m KOH. The FeCoNiP@P‐rGO electrocatalyst exhibits an outstanding durability toward overall water splitting in alkaline electrolytes, and excellent Faraday efficiency (about 92%) as well. This work provides an insight in proper tuning and the development of appropriate substrates for IMPs and other transition metal compounds toward cost‐effective and high efficiency electrocatalysts for water splitting reactions.

Cobalt supported on biomass carbon tubes derived from cotton fibers towards high-efficient electrocatalytic overall water-splitting

Developing noble-metal-free electrocatalysts for high-efficiency oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is still a challenge in the energy conversion application. Herein, a new bifunctional electrocatalyst Co/BCTs is exploited via in-situ growth of metallic Co particles on/in the surface of biomass carbon tubes (BCTs) derived from available natural cotton fibers, which exhibits the outstanding electrocatalytic performance for OER, HER and overall water-splitting. It is because that the mordification effect of Co particles improves conductivity, facilitates electron transfer and activates surface of BCTs, and meanwhile the unique micro- structure and morphology of Co/BCTs can promote the molecular mass transport and shorten the molecular diffusion distance. As expected, the electrolyzer assembled by Co/BCTs-5 as electrode couple attains a very low potential of 1.40 V at 10 mA cm−2 for overall water-splitting in alkaline electrolyte. This work endows new opportunities and potential values for exploiting the high-efficiency noble-metal-free electrocatalysts originated from natural biological derived materials.

Anchoring stable FeS2 nanoparticles on MXene nanosheets via interface engineering for efficient water splitting

Benefiting from an abundant interface with many active sites, robust interaction and synergistic effect between FeS2 and MXene, FeS2@MXene exhibits remarkable catalytic activity towards water splitting in alkaline electrolytes.

Iron and chromium co-doped cobalt phosphide porous nanosheets as robust bifunctional electrocatalyst for efficient water splitting

It is still a huge challenge to develop highly efficient and low-cost non-precious metal-based electrocatalysts for overall water splitting in alkaline electrolytes. Herein, Cr and Fe co-doped CoP porous mesh nanosheets (Mesh-CrFe-CoP NSs) were synthesized through hydrolysis reaction, ion exchange etching and subsequent low-temperature phosphating process. The Mesh-CrFe-CoP NSs provides overpotentials at a current density of 10 mA cm−2 under alkaline electrolyte of 103.7 mV and 256.4 mV for HER and OER, respectively. Furthermore, when using Mesh-CrFe-CoP NSs as anode and cathode, the water splitting system could afford a current density of 10 mA cm–2 at 1.55 V, which is better than an electrolytic cell composed of 20% Pt/C and RuO2. The excellent electrocatalytic performance of Mesh-CrFe-CoP NSs is attributed to the co-doping and porous nanostructure. Specifically, the Cr and Fe co-doped porous CoP nanosheets electrocatalyst not only provided abundant exposure active sites, accelerated the entry of liquid and the diffusion of gas, but also regulated the electronic environment of active sites, and thus enhanced the electrochemical performance. This work proposes a strategy for the rational design of highly efficient and stable non-precious metal co-doped phosphide electrocatalysts in the of electrochemical water splitting.

Systematic constructing CoFe-Prussian blue analogue on NiCo-layered double hydroxide to obtain heterostructure two-bimetallic phosphide composite as efficient self-supported eletrocatalyst for overall water and urea electrolysis

It remains a challenge to explore economical, high-effective and long term stability electrocatalysts toward large-scale hydrogen production. This work utilizes surface engineering strategy to in-situ CoFe-Prussian Blue Analogues on NiCo-layered double hydroxides to obtain 3D hierarchical heterostructure precursor (NiCo–CoFe-PBA). After phosphatization, this precursor can be further transform into tri-metallic phosphide (NiCoP/CoFeP@NF) and directly act as efficient self-supported electrode for Water and Urea Electrolysis. Impressively, the obtained NiCoP/CoFeP@NF-12 (±) electrode shows excellent catalytic performance with only requires the cell voltage of 1.61 and 1.46 V to deliver 10 mA cm−2 in overall water splitting and urea electrolysis, respectively, which benefiting from the porous Ni foam (NF) substrate, large catalytic activity area, remarkable mass/electron transfer property, the synergistic effect of components as well as superhydrophilicity and superaerophobicity of electrode surface. In addition, the experimental results also confirm that urea-assisted system has energy saving advantage superior than traditional water splitting in alkaline electrolyte. Moreover, the hierarchical strategy can also be introduced to the construction of other intricate composites for the utilization in energy conversion and storage.

Earth-Abundant Fe and Ni Dually Doped Co2P for Superior Oxygen Evolution Reactivity and as a Bifunctional Electrocatalyst toward Renewable Energy-Powered Overall Alkaline Water Splitting

In this paper, we report multimetallic phosphide FeNi-Co2P as a superior alkaline oxygen evolution reaction (OER) electrocatalyst and bifunctional electrocatalyst for solar energy-powered water splitting. Fe incorporation into Ni-Co2P leads to (i) the increased amount of high-valence Co3+ and Ni3+, (ii) the improved intrinsic activity of active centers, and (iii) the increased disorder defects in the in situ-formed oxyhydroxide species during the OER activation process. Synergistic actions among them enable the electrocatalyst’s exceptional OER activity with an overpotential of 225 ± 4 mV at 10 mA/cm2, which outperforms the benchmark catalyst RuO2 and most state-of-the-art OER electrocatalysts. Meanwhile, Fe incorporation decreases the density of states near the Fermi level, which slightly degrades the HER activity compared to the Fe-free electrocatalyst. The FeNi-Co2P||FeNi-Co2P and FeNi-Co2P||Ni-Co2P electrolyzer cells demonstrate voltages of 1.596 and 1.578 V at 10 mA/cm2 for water splitting in 1 M KOH, respectively. A solar energy-powered electrolyzer cell for water splitting has been realized with the as-proposed electrocatalysts. Our results suggest that multimetallic phosphides are promising as low-cost, efficient bifunctional electrocatalysts for overall water splitting in alkaline electrolyte. Additionally, this work provides a real-world application scenario of overall water splitting for hydrogen generation by renewable energy sources.

FeOOH-containing hydrated layered iron vanadate electrocatalyst for superior oxygen evolution reaction and efficient water splitting

Abstract A new FeOOH-containing Fe5V15O39(OH)9·9H2O (FVO) has been shown to exhibit superior oxygen evolution reaction (OER) and efficient overall water splitting activities. The critical FeOOH, whose formation is controlled by the surface oxidation state and oxygen vacancy, dominates to improve the OER activity. The co-existence of γ-FeOOH, γ-VOOH, metallic Fe after activation enhances the OER activity. Oxygen vacancy and crystal water have also been shown to enhance the charge transfer. The optimized electrocatalyst gives OER current densities of 10 and 1000 mA cm−2 at excellent overpotentials of 195 and 293 mV, respectively. The electrocatalyst also shows excellent bifunctional performance for full-cell water splitting in alkaline electrolyte, giving a large current density of 1000 mA cm−2 at 2 V and is stable for 85 h. This work provides a new avenue to design an efficient and stable electrocatalyst material with large current density.

High current density electrodeposition of NiFe/Nickel Foam as a bifunctional electrocatalyst for overall water splitting in alkaline electrolyte

Developing highly efficient and inexpensive bifunctional electrocatalysts is a grand challenge in water splitting process. In this article, NiFe electrocatalysts on nickel foam are prepared by electrodeposition method using high current density. The optimized NiFe electrocatalyst presented excellent electrocatalytic activities in 1.0 M KOH medium with low overpotentials of 100 mV for hydrogen evolution reaction and 230 mV for oxygen evolution reaction to achieve 10 mA·cm−2, respectively. Moreover, the optimized NiFe electrocatalyst as bifunctional electrocatalyst toward overall water splitting only needs a small cell voltage of 1.57 V to obtain 10 mA·cm−2. The extremely electrocatalytic performance of NiFe electrocatalyst is attributed to the fast charge transfer kinetics, large electrochemical surface area, and the conductive nickel foam.

Lanthanum doped copper oxide nanoparticles enabled proficient bi-functional electrocatalyst for overall water splitting

The need for a clean and an environmentally non-degrading sustainable energy resource has grown worldwide due to the huge depletion of other fuel sources, as a result, production of hydrogen by electrochemical water splitting is considered as a potential answer to this pertaining need. However, development of low-cost electrocatalyst as a replacement for Pt and RuO2 for both Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) remains a significant challenge for the production of hydrogen at a larger scale. This study presents the synthesis of non-noble metal-based lanthanum doped copper oxide nanoparticles as a potential bi-functional electrocatalyst for overall water splitting in alkaline electrolyte. The optimized 1% lanthanum (La) doped CuO electrocatalyst exhibits outstanding OER and HER activity in 1.0 M KOH electrolyte posting a potential of 1.552 V vs RHE for OER and −0.173 V vs RHE for HER at a current density of ~10 mAcm−2. Significantly, the functional bi-catalyst exhibits a low cell voltage of 1.6 V to achieve overall water splitting at a current density of 10 mAcm−2 along with long-term stability of 13.5 h for a cell voltage of 2.25 V at a constant current density of 30 mAcm−2 with only 20% initial current lose after 13.5 h. The results demonstrate that the incorporation of the rare-earth element onto CuO nanoparticles has made it a viable high-end non-noble electrocatalyst for overall water splitting.

(Invited) Earth-Abundant Ni-Mo-S Based Bifunctional Electrocatalyst for Efficient Water Splitting

Designing and synthesizing proper electrocatalysts with bifunctions for hydrogen and oxygen generation catalytic activity remains a great challenge. In this manuscript, we successfully develop and fabricate an earth abundant Ni-Mo-S based electrocatalyst that is bifunctionally active for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) by water splitting in alkaline electrolyte (1M NaOH). Such an electrocatalyst demonstrates the capability for water splitting in alkaline electrolyte with an applied potential of 1.539 V at the current density of 10 mA/cm2 when used as both anode and cathode. Though detailed studies in the reaction mechanism are still further required, the results suggest that the geometrical high surface area and the modified electronic structures and surface chemistry are very important in designing bifunctional electrocatalysts.