Electrodes For Water Splitting Research Articles

Cobalt Doped Sulfonated Polyaniline with High Electrocatalytic Activity and Stability for Oxygen Evolution Reaction

AbstractThe oxygen (OER) evolution reaction plays a crucial role for storage of renewable energy sources but, active sites of the active electrocatalysis remain in challengeable. In this work, we have developed sulfonated polyaniline (SPANI) coordinated with Co sites to investigate the OER process. To improve the electrical conductivity and electrocatalytic efficiency towards OER herein, we report Co@SPANI synthesized by solvothermal method. The different physical characterization (SEM, TEM, XRD, IR, XPS and UV‐DRS) and electrochemical methods (voltammetry, chronopotentiometry and EIS) have been used to characterize Co@SPANI materials and examined the correlation of materials with activity. The cobalt doped SPANI (Co@SPANI‐800) exhibits higher electrocatalytic activity, showing smaller Tafel slope of 167 mV dec−1 with lower overpotential of 312 mV at 10 mA cm−2 in 1 M KOH, which reveal that abundant Co‐metal sites remarkably supporting the OER activity. Co@SPANI‐800 exhibits exceptional OER performances and durability over 200 h with loss of <3.5 % in alkaline medium. At 1.54 V, solar powered water electrolysis confirmed the effectiveness of newborn electrocatalyst in solar energy to hydrogen energy conversion. Therefore, this work offered new path for designing materials as self‐supporting electrode for water splitting and for other potential applications.

One-Dimensional CoMoP Nanostructures as Bifunctional Electrodes for Overall Water Splitting.

As high-quality substitutes for conventional catalysts, the bifunctional catalytic properties of the coating of transition-metal-based materials are pivotal for improving water-splitting efficiency. Herein, cobalt-molybdenum bimetallic phosphide nanofibers (CoMoP NFs) were synthesized via a series of facile strategies, which are divided into pyrolysis electrospun PAN and metal salts, to obtain one-dimensional morphology and a gas-solid phosphating precursor. The obtained CoMoP NFs catalyst has superior catalytic activity performance in 1M KOH. Serving as an oxygen evolution reaction (OER) catalyst, the electrode of the CoMoP NFs affords different kinds of current densities at 50 mA cm-2 and 100 mA cm-2, with low overpotentials of 362 and 391 mV, respectively. In addition, the hydrogen evolution reaction (HER) performance of the CoMoP NFs mainly shows when under a low overpotential of 126 mV, which can deliver a current density of 10 mA cm-2. In order to further detect the stability of the catalyst, we used multiple cyclic voltammetry and chronopotentiometry tests for OERs and HERs, which maintain performance and carry a current density of 10 mA cm-2 for longer. As an integrated high-performance bifunctional electrode for overall water splitting, the CoMoP NFs only require 1.75 V@10 mA cm-2 for 40 h. This work highlights a facile method to create an electrocatalyst with fiber nanostructures which possesses excellent activity as an alkaline electrolyte.

Optimizing band structure of CoP nanoparticles via rich‐defect carbon shell toward bifunctional electrocatalysts for overall water splitting

AbstractTransition‐metal phosphides (TMPs) with high catalytic activity are widely used in the design of electrodes for water splitting. However, a major challenge is how to achieve the trade‐off between activity and stability of TMPs. Herein, a novel method for synthesizing CoP nanoparticles encapsulated in a rich‐defect carbon shell (CoP/DCS) is developed through the self‐assembly of modified polycyclic aromatic molecules. The graft and removal of high‐activity C–N bonds of aromatic molecules render the controllable design of crystallite defects of carbon shell. The density functional theory calculation indicates that the carbon defects with unpaired electrons could effectively tailor the band structure of CoP. Benefiting from the improved activity and corrosion resistance, the CoP/DCS delivers outstanding difunctional hydrogen evolution reaction (88 mV) and oxygen evolution reaction (251 mV) performances at 10 mA cm−2 current density. Furthermore, the coupled water electrolyzer with CoP/DCS as both the cathode and anode presents ultralow cell voltages of 1.49 V to achieve 10 mA cm−2 with long‐time stability. This strategy to improve TMPs electrocatalyst with rich‐DCS and heterogeneous structure will inspire the design of other transition metal compound electrocatalysts for water splitting.

Ligand‐Engineered Quantum Dots Decorated Heterojunction Photoelectrodes for Self‐Biased Solar Water Splitting (Small 46/2022)

Bias-Free Water Splitting In article number 2204495, Xin Tong, Lianzhou Wang, Zhiming M. Wang, and co-workers develop a quantum dots (QDs)-based photoelectrochemical (PEC) device comprised of tandem Zn-doped CuInS2 QDs-decorated metal oxide electrodes (BiVO4 and Cu2O) for bias-free solar water splitting. Both the ligands capped on QDs and QDs-electrode heterojunctions are rationally engineered to promote the photo-induced charge transfer in the PEC system, delivering a solar-to-hydrogen efficiency of 0.65% with excellent stability.

Mild Construction of "Midas Touch" Metal-Organic Framework-Based Catalytic Electrodes for Highly Efficient Overall Seawater Splitting.

Mild construction of highly efficient and durable practical electrodes for overall water splitting (OWS) at industrial-grade current density is currently a significant challenge. Herein, metal-organic framework (MOF) materials are grown in situ on the surface of carbon cloth (CC) at 25 °C, and quickly "interspersed" by cobalt-boron (Co-B) via electroless plating for 30min to obtain a highly efficient and stable CoB@MOF@CC self-supporting electrode. Owing to the large specific surface area, abundant active sites, and porous structure, the MOF-based CC modified by bamboo leaf-like ultrathin CoB has remarkable electrochemical catalysis efficiency. The CoB@MOF@CC electrode exhibits excellent performance during the hydrogen evolution reaction (η10 = 57mV, η500 = 266mV) and oxygen evolution reaction (η10 = 209mV, η500 = 423mV) in alkaline simulated seawater, and is durable for 2500h at 500mA cm-2 . The OWS performance is obviously enhanced by employing the prepared electrode, which only requires 1.49V to achieve 10mA cm-2 and is durable for over 360h at industrial-grade current densities in alkaline high-salt, real seawater, rainwater, and urea electrolytes.

Synergizing Cobalt Ruthenium Alloy with Chromium Oxyhydroxide for Highly Efficient Electrocatalytic Water Splitting.

Constructing a coupling interface of multicomponents with different functions is of considerable importance for designing an advanced bifunctional water splitting electrode. Particularly, designing and developing alloy/oxyhydroxide-integrated electrodes have emerged as a tendency yet remain a considerable challenge. In this work, a novel 3D nanostructure electrocatalyst assembled from CoRu nanoalloy and CrOOH nanosheets (denoted as CoRu-CrOOH/NF) was directly grown on nickel foam via a successive hydrothermal method. The unique synergy in CoRu-CrOOH/NF heterostructures is not only conducive to strengthening charge transfer capability and accelerating the reaction kinetics but also favors the redistribution of charge within the interface, thus improving the electrocatalytic performance. In view of the above-mentioned points, the resultant CoRu-CrOOH/NF displays outstanding catalytic performance with overpotentials of 26 and 272 mV at 10 mA cm-2 for hydrogen evolution reaction (HER) and 50 mA cm-2 for oxygen evolution reaction (OER). Remarkably, the symmetrical two-electrode cell using CoRu-CrOOH/NF only acquires 1.47 V at 10 mA cm-2 in 1.0 M KOH, which is superior to many other state-of-the-art overall water-splitting electrocatalysts. This holistic work provides a new insight to designing alloy/oxyhydroxide-integrated electrodes for high-efficiency overall water splitting.

Non-precious metal-based integrated electrodes for overall alkaline water splitting

A bifunctional electrocatalyst interface requires a superior charge transfer and good electric conductivity to produce an efficient and stable water splitting reaction. In the context of controlling the electrochemical activity of bifunctional catalytic materials, we demonstrate a novel approach to bridge conductive C-Qd-Mn interfaces with precise control. The excellent performance for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) can be dominantly attributed to the unique structure of C-Qds-Mn, which provides abundant active sites and facilitates electron transfer between electrode and electrolyte. Eco-friendly C-Qds were synthesized using a large-scale thermal assisted technique and utilized as electrocatalysts with Mn3O4 in alkaline splitting ToF (Turn over Frequency) calculation to make an effective combination. Due to their increased ECSA, conductivity, and electron-hole transfer, the prepared C-Qds-Mn delivered excellent HER/OER (0.494 V/1.6671V) activity, lower Standard deviation 0.006 V and 0.009V, surpassing the 10 mA limit comparable to commercially.

Ternary FeCo2Mo5 Oxyhydroxide Nanosheets Integrate on the Surface-Vulcanized Ni Foam for Excellent Electrocatalytic Oxygen Evolution

Earth-abundant first-row transition-metal-based electrocatalysts with a large current density for water splitting are pivotal to give impetus to large-scale utilization of hydrogen energy. However, the operating potential is significantly larger than the thermodynamic requirements. Herein, the ternary FeCo2Mo5 layered double hydroxide (LDH) nanosheets grown on the surface of a vulcanized Ni foam (FeCo2Mo5 LDH/Ni3S2/NF) are proposed to improve the mass and electron transport for driving the oxygen evolution reaction (OER), where the integrated hierarchical structure configurations contribute rich active sites and a large electrode/electrolyte interface for mass transfer, and the construction of a Ni3S2/NF heterojunction can facilitate electron mobility from the surface to the inner region, leading to a high valence of FeCo2Mo5 LDH with favorable OER kinetics. Therefore, the catalyst exhibits excellent OER activity with the ultralow overpotential of 128 and 300 mV at the current density of 10 and 100 mA cm–2 in 1 M KOH and activity retention over 12 h at 95 mA cm–2. This research may enable a large extension toward the design of cheap and highly efficient practical catalytic electrodes for water splitting.

Application of Reverse Electrodialysis Power for Oxygen Generation in Undersea Diving

With continued growth of marine exploration and underwater missions, there is a need to design new diving technologies. Currently, dive time is limited by scuba tank weight and volume. The use of an electrolysis system, powered by a battery, for driving chemical reactions could be introduced to produce a steady supply of oxygen during dives. However, batteries have a limited capacity, are heavy, and are detrimental to the environment when disposed. Developing an electrochemical technology that utilizes resources abundantly available to a diver (salt water) to drive the oxygen evolution reaction would expand the duration and sustainability of ocean dives. Reverse electrodialysis (RED) is a multi-membrane system that aims to convert salinity gradient energy into electrical energy. Redox mediators are typically used to convert ionic mixing into electricity at electrodes placed adjacent to a stack of membranes. However, replacing redox mediators with water splitting electrodes can enable the sustainable production of fuel (H2) and/or oxygen (O2). We aim to examine if a RED oxygen generation system could meet oxygen requirements for scuba diving. Evolving oxygen from water would enable the development of artificial gills, allowing for an inexhaustible supply of oxygen thus displacing the need to carry oxygen tanks. Here we propose a system where instead of an air tank, a diver carries a RED cell, a 2 L volume of dilute solution, and a cylinder of other compressed gases for breathing (Fig. 1a). A RED cell is comprised of a stack of alternating anion and cation exchange membranes separated by channels of high and low concentration solutions (HC and LC) (Fig. 1b). A stack is made up of repeating units, which consist of a pair of selective membranes and a pair of solution channels, between the anode and cathode chambers. Salt ions in solution migrate due to the concentration gradient and two redox based electrodes convert this ionic flux into electric flux. We show here that the oxygen evolution activation overpotentials are a significant fraction of internal resistance (77%) in a RED system with a small number of cell pairs (N=5). However, this resistance is nearly negligible (3.2%) as the number of cell pairs increases (N=500). We further compare the RED systems to four different battery-electrolysis systems (Li-ion, Ni-MH, Ni-Cd, and lead acid) to contextualize the performance of the RED oxygen generation system with competing technologies. For large (N=100+) systems and long (10 hr) dives, RED is comparable in size to a battery-electrolysis system. With 500 membrane pairs, a RED powered diving system is 10.8 L and weighs 29 kg. Typical 12 L scuba tanks weigh 16 kg, and the size of a Li-ion battery powered electrolysis system for a 1 hour dive is, 2.2 L and 3.5 kg (19.2 L and 32.6 kg for a 10 hour dive).Figure 1. (a) Configuration of a RED cell for scuba divers using the surrounding seawater, a fixed dilute volume, and a fixed volume of additional gases for breathing carried by the diver. (b) Schematic of RED cell. Oxygen and hydrogen are produced at the anode and cathode by redox reactions. Figure 1

Steady State Performance Evaluation of Noble-Metal Free Bifunctional Electrode for Overall Water Splitting

The emerging need of clean and renewable energy drives the exploration of effective strategies to produce molecular hydrogen. With the assistance of highly active non-noble metal electrocatalysts, electrolysis of water is becoming a promising candidate to generate pure hydrogen with low cost and high efficiency. This reaction takes place almost exclusively on Pt/C catalysts at the cathode which is expensive and need to be replaced by a metal-based catalyst that is cost effective and can show a comparable HER (Hydrogen Evolution Reaction) activity. Transition metal oxides, nitrides and sulfides have been widely explored as catalysts for HER and OER (Oxygen Evolution Reaction) due to their good electronic conductivity, stable and variable oxidation states, and superior corrosion resistance. In this research, MoNi4 embedded MoO3 nanorods are synthesized using facile hydrothermal method. Further, Molybdenum Vanadium Nitride is coated on top the synthesized electrode using RF/DC magnetron co-sputtering. This combination of hydrothermal and magnetron sputtering fabrication methods of the electrodes results in high surface area of the electrodes thereby improving the reaction kinetics of hydrogen production. The performance of the electrodes is tested in N2/O2 saturated 1M KOH solution using steady state technique called Staircase Voltammetry (SCV) instead of conventional dynamic LSV (Linear Sweep Voltammetry)/CV (Cyclic Voltammetry). This alternative method for testing is performed due to the exaggeration of the catalytic performance through conventional LSV/CV arising from double layer charging for nanostructured electrode. The electrodes are characterized by X-ray diffraction and SEM for structural and morphological analysis. Hence, we report the synthesis of novel MoVN on MoNi4/MoO2 nanorods using DC/RF Magnetron co-sputtering as an efficient, bifunctional, binder free electrode for overall water splitting. The electrode is characterised for both full-cell and half-cell configurations proving its stability for 12 hours. This work provides a reliable approach to the production of low cost and high-effectiveness electrodes for the application in commercial electrolyzers.

Engineering Transition Metals As Noble-Metal Free Bifunctional Electrode for Overall Water Splitting

The emerging need of clean and renewable energy drives the exploration of effective strategies to produce molecular hydrogen. With the assistance of highly active non-noble metal electrocatalysts, electrolysis of water is becoming a promising candidate to generate pure hydrogen with low cost and high efficiency.[1] This reaction takes place almost exclusively on Pt/C catalysts at the cathode which is expensive and need to be replaced by a metal-based catalyst which can show a comparable HER (Hydrogen evolution reaction) activity. Transition metal oxides, nitrides and sulfides have been widely explored as catalysts for HER and OER (Oxygen evolution reaction) due to their good electronic conductivity, stable and variable oxidation states, and superior corrosion resistance.[2] In this research, MoNi4 embedded MoO3 nanorods are synthesized using facile hydrothermal method. Further, Molybdenum Vanadium Nitride is coated on top the synthesized electrode using RF/DC magnetron co-sputtering.[3] This combination of hydrothermal and magnetron sputtering fabrication methods of the electrodes results in high surface area of the electrodes thereby improving the reaction kinetics of hydrogen production. The performance of the electrodes is tested in N2/O2 saturated 1M KOH solution using steady state technique called Staircase Voltammetry (SCV) instead of conventional dynamic LSV (Linear sweep voltammetry)/CV (Cyclic Voltammetry).[4] This alternative method for testing is performed due to the exaggeration of the catalytic performance through conventional LSV/CV arising from double layer charging for nanostructured electrode. The electrodes are characterized by X-ray diffraction and SEM for structural and morphological analysis. Hence, we report the synthesis of novel MoVN on MoNi4/MoO2 nanorods using DC/RF Magnetron co-sputtering as an efficient, bifunctional, binder free electrode for overall water splitting. The electrode is characterised for both full-cell and half-cell configurations proving its stability for 12 hours. This work provides a reliable approach to the production of low cost and high-effectiveness electrodes for the application in commercial electrolyzers.[1] J. Zhang et al., “Efficient hydrogen production on MoNi4 electrocatalysts with fast water dissociation kinetics,” Nat. Commun., vol. 8, no. May, pp. 1–8, 2017, doi: 10.1038/ncomms15437.[2] L. A. Santillán-Vallejo et al., “Supported (NiMo,CoMo)-carbide, -nitride phases: Effect of atomic ratios and phosphorus concentration on the HDS of thiophene and dibenzothiophene,” Catal. Today, vol. 109, no. 1–4, pp. 33–41, 2005, doi: 10.1016/j.cattod.2005.08.022.[3] B. Wei et al., “Bimetallic vanadium-molybdenum nitrides using magnetron co-sputtering as alkaline hydrogen evolution catalyst,” Electrochemistry Communications, vol. 93. pp. 166–170, 2018, doi: 10.1016/j.elecom.2018.07.012.[4] S. Anantharaj and S. Kundu, “Do the Evaluation Parameters Reflect Intrinsic Activity of Electrocatalysts in Electrochemical Water Splitting?,” ACS Energy Lett., vol. 4, no. 6, pp. 1260–1264, 2019, doi: 10.1021/acsenergylett.9b00686. Figure 1

Bifunctional petal-like carbon–nitrogen covered NiFeOx/nickel foam nanohybrid electrocatalyst for efficient overall water splitting

• Carbon-nitrogen doped NiFeO x catalysts was prepared by using NiFe-LDH as a precursor to induce the formation of mixed metal oxide with high metal dispersibility. • The interlayer accumulation of bulk NiFe-LDH was dispersed by 2-methylimidazole hydrothermal reaction, and the transfer efficiency of proton receptor was improved. • The carbon coating with EDTA as organic carbon source improves the stability of the NiFeO x N C catalyst. • The NiFeO x N C has stable and remarkable behaviors for water splitting. • The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. NiFe-based compounds have attracted increasing attention due to their availability and excellent catalytic performance for the hydrogen evolution (HER) and oxygen evolution reaction (OER). Based on the structure of bulk NiFe-LDH, dispersed interlayer stacking facilitates the diffusion of proton receptors and expose more active sites. Then, nitrogen and graphite domains are controllably introduced by carbonization to improve the conductivity. In this paper, carbon–nitrogen covered NiFeO x was prepared by carbonizing the modified precursor, NiFe layered double hydroxide (NiFe-LDH) with ethylenediaminetetraacetic acid (EDTA). The as-synthesized NiFe EDTA exhibits good bifunctional activity with overpotentials of 163 mV and 249 mV to achieve current densities of 10 mA·cm −2 in 1.0 M KOH for HER and OER, respectively, which is ascribed to the structural advantages of polycrystalline interface and carbon encapsulation structure. Moreover, by using NiFe EDTA as cathode and anode electrodes for overall water splitting (OWS), the cell voltage only needs 1.51 V at 10 mA·cm −2 . The NiFe EDTA has good OWS stability and works at 1.6 V for 70 h.

Fabrication and evaluation of a self-standing reduced graphene-tungsten oxides hybrid electrode for acidic water splitting

Efficient and sustained hydrogen production via acidic water splitting is of great importance in the electrolyzer industry. Here, we have designed and synthesized a self-assembled, freestanding, three dimensional (3D) reduced graphene-non-noble tungsten oxide (SA-GWO) electrode with high comprehensive acidic electrolysis performance. Adsorption isotherm suggested the formation of mesoporous structural design within a 3D self-assembled SA-GWO architecture electrode. Bi-functional (HER and OER) activity has been displayed by SA-GWO electrodes at the combined full potential of 1.9 V and attains the standard 10 mA/cm2 (1 M H2SO4, 28 °C). Remarkably, it exhibits OER activity in the acidic medium, which is so far very limited. The tafel slope and the exchange current density for the HER process are observed to be 117 mV/decade and 1.73 × 10−3 mA/cm2, respectively, at 28 °C. Importantly, the production rate of hydrogen is found to increase with increasing temperature. HER is highly dominated by the Volmer route. Gas liberated at the respective electrode has been tested via gas chromatography (GC) analysis. SA-GWO supports the faradaic efficiency of 73 and 52% for HER and OER, respectively. Tafel slope for OER appeared to be very high owing to its complex mechanistic pathway. Disintegration of 3D monoclinic WO3 and the formation of 2D nanochannels like nanostructure have been distinctly observed in SEM micro images, when the electrode is subjected to cathodic HER reaction (−0.5 V, 1 M H2SO4). Most importantly, the WO3 polymorph typically responsible for the distinct mechanism of HER and OER action in 1 M H2SO4 has been identified and proven. Moreover, the 3D SA-GWO electrode as HER possesses great endurance and incomparable stability in acidic media.

3D well-ordered wood substrate coupled transition metal boride as efficient electrode for water splitting

The choice of substrate is critical to the performance of binder-free electrode for water splitting. Here, carbonized wood is employed as 3D porous diffusion substrates to accommodate conductive transitional metal boride. The composite is efficiently and uniformly deposited on the inner wall of the carbonized wood by means of simple electroless plating technique. The well-defined 3D Ni-W-B/wood electrode requires overpotential of only 46 mV at 50 mA cm−2 for hydrogen evolution reaction (HER), outperforming the Ni-W-B/NF electrode with nickel foam as the substrate. The ordered channel structure inherited from the carbonized wood endows the electrode with abundant active site density, fast mass and charge transportation, and efficient transport of evolved gas. The outstanding advantages of environmentally benign nature, low cost, favorable 3D channel structure, and anti-corrosion in harsh condition make wood as a promising substrate for binder-free electrode.

Amorphized core–shell NiFeMo electrode for efficient bifunctional water splitting

To effectively alleviate the realistic pressure of carbon emissions, electrocatalytic water splitting to produce hydrogen has broadened people's access to obtain clean energy. However, the development of low-cost, high-efficiency bifunctional electrode is a technical bottleneck to improve the overall water splitting performance. Based on the above problems, a bifunctional electrode material in which amorphous NiFeMo films assembled with the core–shell structure were in-situ grown on a conductive nickel foam substrate (NiFeMo/NF). Thanks to the synergistic effect multi-atoms containing Ni, Fe and Mo and abundant active sites brought by the amorphous structure, the resulted NiFeMo compounds displayed the overpotential of 215 mV and 180 mV for OER and HER at 10 mA cm−2, respectively. What's more, couple electrodes composed of NiFeMo/NF only requires the voltage of 1.62 V (vs. RHE) to gain 10 mA cm−2 in an overall water-splitting device and along with excellent stability for more than 100 h in alkaline medium. This work provides an idea to explore new generation of high-efficiency electrodes.

Highly durable, Pt free and large-area Ni–B film synthesized by SILAR as a bifunctional electrode for electrochemical water splitting

A search for efficient, durable, large-area, and economic catalyst material for low-cost production of hydrogen and oxygen is currently a high priority in the field of electrocatalysis (EC). In view of this, a cost-effective, earth abundant, highly stable, Pt free, and large-area (8 cm × 8 cm) bifunctional Ni–B electrocatalyst is reported via simple and economic SILAR method. A highly porous surface of Ni–B film with high surface wettability indicated better electrochemical water-splitting properties for the films and is obtained at 100 cycles. A Low over-potential value to obtain HER (49 mV) and OER (340 mV) at 10 mA/cm2 current suggested that they are comparable to the well-known Pt and RuO electrodes in alkaline medium (1M KOH), respectively. In actual water-splitting setup having Ni–B film (as cathode) and stainless steel (as anode), the hydrogen production of 612 ml/h is obtained at constant potential, which was enhanced by 18% i.e., 726 ml/h when a Ni–B film as both cathode and anode electrode was used. Both the electrodes are highly stable for over 15 days and interestingly they showed 7% increment in the EC performance.

Cover Image, Volume 4, Number 4, June 2022

Front cover image: Discovering the creative multifunctional potential of a single material is an essential criterion for formulating highly efficient energy storage and conversion systems. In article number 10.1002/cey2.207, Uk Sim and co-workers report the development of sulfur self-doped biochar (SA-Came) derived from the Camellia Japonica flowers as a multifunctional electrode for overall water splitting and supercapacitor application.

TiN ceramic membrane supported nitrogen-incorporating NiCo2 nanowires as bifunctional electrode for overall water splitting in alkaline solution

Developing a highly efficient, cost-effective, and stable bifunctional electrode for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is still a major challenge. This work reports on a novel method for fabricating TiN ceramic membrane supported nitrogen-incorporating NiCo2 nanowires (NiCo2-N/TiN) as a bifunctional electrode. Owing to its unique structure, the ample reaction sites available, and the enhanced mass/charge transport ability, the NiCo2-N/TiN electrode exhibits efficient catalytic performance both in HER and OER, with overpotentials of 131 mV at 20 mA·cm−2 for HER and 330 mV at 20 mA·cm−2 for OER, together with excellent stability in alkaline solution. The NiCo2-N/TiN electrode only requires a cell voltage of 1.71 V to drive the current density of 20 mA·cm−2 for overall water splitting, which exhibits excellent stability for more than 100000 s. Accordingly, the produced ceramic membrane electrode has a great potential for application in industrial hydrogen production.

Phosphorus-doping promotes the electrochemical etching of metals to nanoporous electrodes for efficient and durable overall water splitting

Electrocatalysts play a central role in electrochemical water splitting to store renewable energy in the chemical fuel of hydrogen. Nanoporous metal electrodes are promising to boost hydrogen production efficiency while challenging in synthesis. Here, a phosphorus-doping assisted electrochemical etching strategy is developed to construct highly nanoporous surfaces on metal electrodes, leading to a remarkable catalytic performance for overall water splitting under lab-level or industrial electrolysis conditions. Specifically, the nanoporous FeCoNiCu foil shows 46 times higher electrochemical surface area, lowering the overpotentials by 102 mV for oxygen evolution reaction and 157 mV for hydrogen evolution reaction. The viability of the strategy is further demonstrated in the prevailing industrial electrodes of nickel meshes, enabling a cell voltage of only 1.931 V under the harsh industrial electrolytic condition (80 °C, 30 wt% KOH, and a current density of 500 mA cm−2). It is 126 mV lower than that of a bare nickel mesh-based electrolyzer and corresponds to a ∼4% improvement in energy-conversion efficiency. This work offers a facile and ease-to-scale-up approach for the upgrading of widespread metal electrodes, possessing great prospects in energy conversion and storage devices including electrolyzers, fuel cells, batteries, and supercapacitors.

Hierarchical Metal Sulfides Heterostructure as Superior Bifunctional Electrode for Overall Water Splitting.

The development of highly active bifunctional electrocatalysts for overall water splitting is of significant importance, but huge challenges remain. The key element depends on engineering the electronic structure and surface properties of material to achieve improved catalytic activity. Herein, a hierarchical nanowire array of metal sulfides heterostructure on nickel foam (FeCoNiSx /NF) was designed as a novel type of hybrid electrocatalyst for overall water splitting. The hybrid structure endowed plenty of catalytic active sites, strong electronic interactions, and high interfacial charge transferability, leading to superior bifunctional performance. As a result, the FeCoNiSx /NF catalyst delivered low overpotentials of 97 and 260 mV at the current density of 50 mA cm-2 for hydrogen and oxygen evolution reactions, respectively. Moreover, the FeCoNiSx /NF-based water electrolyzer exhibited a small potential of 1.57 V for a high current density of 50 mA cm-2 . These results indicate the promising application potential of FeCoNiSx /NF electrode for hydrogen generation. This work provides a new approach to develop robust hybrid materials as the highly active electrode for electrocatalytic water splitting.