Co3O4 nanoparticles decorated Polypyrrole/carbon nanocomposite as efficient bi-functional electrocatalyst for electrochemical water splitting

An effective bi-functional electrocatalyst of Co₃O₄/Polypyrrole/Carbon (Co₃O₄/Ppy/C) nanocomposite was prepared through a simple dry chemical method and used to catalyze the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Three types of carbon support as Vulcan carbon, reduced graphite oxide (RGO) and multi-walled carbon nanotubes (MCNTs) were used to study the influence on electrochemical reactions. Spherical shaped Co₃O₄ nanoparticles with 8–10 nm was found uniformly distributed on Ppy/C composite, which were analyzed by X-ray diffraction and transmission electron microscopy techniques. Amongst, Co₃O₄/Ppy/MWCNT shows improved bifunctional electrocatalytic activity towards both OER and HER with relatively low over potential (340 mV vs. 490 mV at 10 mA cm⁻²) and Tafel slope (87 vs. 110 mV dec⁻¹). In addition to that, MWCNT supported Co₃O₄/Ppy nanocomposite exhibits good electronic conductivity and electrochemical stability up to 2000 potential cycles. The results clearly indicate that the Co₃O₄/Ppy/MWCNT nanocomposite could be the promising bi-functional electrocatalyst for efficient water electrolysis.     

Chromium doping and in-grown heterointerface construction for modifying Ni3FeN toward bifunctional electrocatalyst toward alkaline water splitting

Exploring high-performance non-noble metal electrocatalysts is pivotal for eco-friendly hydrogen energy applications. Herein, featuring simultaneous Chromium doping and in-grown heterointerface engineering, the Cr doping Ni₃FeN/Ni heterostructure supported on N-doped graphene tubes (denoted as Cr–Ni₃FeN/Ni@N-GTs) was successfully constructed, which exhibits the superior bifunctional electrocatalytic performances (88 mV and 262 mV at 10 mA cm⁻² for HER and OER, respectively). Furthermore, an alkaline electrolyzer, employing Ni₃FeN/Ni@N-GTs as both the cathode and the anode, requires a low cell voltage of 1.57 V at 10 mA⋅cm⁻². Cr doping not only modulates the electronic structure of host Ni and Fe but also synchronously induces nitrogen vacancies, leading to a higher number of active sites; the in-grown heterointerface Cr–Ni₃FeN/Ni induces the charge redistribution by spontaneous electron transfer across the heterointerface, enhancing the intrinsic catalytic activity; the N-GTs skeleton with excellent electrical conductivity improves the electron transport and mass transfer. The synergy of the above merits endows the designed Cr–Ni₃FeN/Ni@ N-GTs with outstanding electrocatalytic properties for alkaline overall water splitting.     

Combustion-derived BaNiO3 nanoparticles as a potential bifunctional electrocatalyst for overall water splitting

Electrochemical water electrolyser though an assuring solution for clean hydrogen production, the sluggish kinetics and high cost of existing precious metal electrocatalyst remains a barrier to its effective utilization. Herein, solution combustion route derived perovskite type barium nickelate (BaNiO₃) nanoparticles were developed and studied for their bifunctional electrocatalytic properties towards overall water splitting. The unannealed BaNiO₃ nanoparticles exhibited the highest OER and HER activity with overpotentials 253 mV and 427 mV respectively to attain 10 mAcm⁻² in 1.0 M KOH. Using unannealed BaNiO₃ as a bifunctional electrocatalyst in a two-electrode alkaline electrolyser, the cell was able to achieve the benchmark current density at a low cell voltage of 1.82 V. Impressively the setup's electrocatalytic performance improved 4.9% after continuous overall water splitting for 24 h at 30 mAcm⁻². Therefore, BaNiO₃ nanoparticles can be a low-cost and efficient alternative for noble metal electrocatalysts for clean H₂ production.     

Co incorporated Ni3S2 hierarchical nano/micro cactus for electrochemical water splitting

Hierarchical nano/micro Ni₃S₂ cactus like structures were fabricated using cost effective and eco-friendly hydrothermal technique. Both pure and Co:Ni₃S₂ composite nanostructures were grown on nickel foam under different synthesis temperatures. The synthesized nanostructures showed a wide variation of hierarchical morphology with variation of synthesis temperatures. The obtained nanostructures were investigated for electrochemical water splitting performance. The morphologies of the samples were found to acquire higher aspect ratio with increment in synthesis temperature. This morphological tuning led to remarkable enhancement in hydrogen evolution performance with very low overpotential 206 mV at 100 mA cm⁻² in acidic medium. Owing to this superior morphology tuned water splitting performance, this low dimensional Ni₃S₂ system can be recognized as potential leader in electrochemical energy harvesting sector.     

Bimetallic-metal organic framework-derived Ni3S2/MoS2 hollow spheres as bifunctional electrocatalyst for highly efficient and stable overall water splitting

Herein, strongly coupled Ni₃S₂/MoS₂ hollow spheres derived from NiMo-based bimetal-organic frameworks are successfully synthesized for overall water splitting via a one-pot solvothermal method followed by sulfurization. A well-defined hollow spherical structure with a heterointerface between Ni₃S₂ and MoS₂ is constructed using solvothermal and sulfurization processes. Owing to their bimetallic heterostructure, porous hollow carbon structure with large surface area, and numerous exposed active sites, the Ni₃S₂/MoS₂ hollow spheres are found to be efficient electrocatalysts for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The heterostructured Ni₃S₂/MoS₂ hollow spheres show small overpotentials of 303 and 166 mV to reach a current density of 10 mA cm^?2 for the OER and HER in 1.0 M KOH, respectively. Furthermore, an overall water-splitting electrolyzer consisting of the Ni₃S₂/MoS₂ hollow spheres as both the anode and cathode requires a very low cell voltage of 1.62 V to drive a current density of 10 mA cm^?2 with outstanding long-term stability for 100 h. Our findings offer a new pathway for the design and synthesis of electrochemically advanced bifunctional catalysts for various energy storage and conversion applications.     

1T/2H MoS2/MoO3 hybrid assembles with glycine as highly efficient and stable electrocatalyst for water splitting

Despite great efforts have been made during the past decade to improve the efficiency of hydrogen evolution reaction (HER) onto the MoS₂-based electrocatalysts via increasing the number of active sites, further improvements are crucial to avoid the detachment of 2D MoS₂ nanosheets from the substrate during the long-term water splitting under intense HER. In this study, we report on the formation of highly efficient and surprisingly stable layer composed of 2D nanoplatelets from the hybrid-type MoS₂ as a new prospective electrocatalyst for HER from acidic water solution. This layer was formed via one-pot hydrothermal synthesis in the solution containing ammonium heptamolybdate, thiourea and glycine (Gly). The products obtained were characterized by SEM, HRTEM, XRD, Raman, XPS, and potential cycling. Note that at the designed hybrid-type MoS₂/MoO₃-Gly nanoplatelets the HER rate can achieve a stable electrochemical performance for days with ~100 mA cm⁻² current density at −0.35 V potential vs RHE.     

Pd/PdO and hydrous RuO2 difunction-modified SiO2@TaON@Ta3N5 nano-photocatalyst for efficient solar overall water splitting

A novel Pd/PdO and hydrous RuO₂ difunction-modified SiO₂@TaON@Ta₃N₅ core-shell structured nano-photocatalyst was synthesized successfully, which displayed excellent photocatalytic activity for overall water splitting into H₂ (473.52 μmol⁻¹·g⁻¹·h⁻¹), about 2.86 times higher than unmodified SiO₂@TaON@Ta₃N₅ (165.74 μmol⁻¹·g⁻¹·h⁻¹), under the visible-light irradiation with the wavelength ≥420 nm, without any sacrificial agent, as well as excellent stability against photocorrosion. The apparent quantum yield (AQY) reaches to 0.253% under irradiation intensity of 12 mW cm⁻² at 420 nm. The spatially separated Pd, PdO and RuO₂ clusters were decorated on the Ta₃N₅ surface to construct local multi-heterojunctions, which were confirmed to enhance the light absorption capability, drive efficient separation of charge carriers and directional transfer, and promote surface redox reaction kinetics of HER and OER. The trace modification of metallic Pd clusters and TaN could mainly contribute to the significant decrease in the HER overpotential, while PdO exhibited a stronger contribution than RuO₂ for OER catalytic activity. The synergetic mechanism of enhanced photocatalytic overall water splitting for hydrogen production was discussed in detail. Thus the combination of core-shell heterojunction construction and surface difunction modification provides a promising strategy for develop efficient all-in-one photocatalysts for solar overall water splitting.     

In-situ growth of Ni–CoSe2 on biomass-derived carbon tubes as an efficient electrocatalyst for overall water splitting

A Ni–CoSe₂/BCT composite composed of biomass-derived carbon tubes and transition metal selenides was successfully constructed and explored as a highly efficient bifunctional electrocatalyst for overall water splitting.

1. Download : Download high-res image (184KB)
2. Download : Download full-size image

     

Efficient overall water splitting over a Mo(IV)-doped Co3O4/NC electrocatalyst

To meet the demand of producing hydrogen at low cost, a molybdenum (Mo)-doped cobalt oxide (Co₃O₄) supported on nitrogen (N)-doped carbon (x%Mo–Co₃O₄/NC, where x% represents Mo/Co molar ratio) is developed as an efficient bifunctional electrocatalyst for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). This defect engineering strategy is realized by a facile urea oxidation method in nitrogen atmosphere. Through X-ray diffraction (XRD) refinement and other detailed characterizations, molybdenum ion (Mo⁴⁺) is found to be doped into Co₃O₄ by substituting cobalt ion (Co²⁺) at tetrahedron site, while N is doped into carbon matrix simultaneously. 4%Mo–Co₃O₄/NC is the optimized sample to show the lowest overpotentials of 91 and 276 mV to deliver 10 mA cm^?2 for HER and OER in 1 M potassium hydroxide solution (KOH), respectively. The overall water splitting cell 4%Mo–Co₃O₄/NC||4%Mo–Co₃O₄/NC displays a voltage of 1.62 V to deliver 10 mA cm^?2 in 1 M KOH. The Mo⁴⁺ dopant modulates the electronic structure of active cobalt ion (Co³⁺) and boosts the water dissociation process during HER, while the increased amount of lattice oxygen and formation of pyridinic nitrogen due to Mo doping benefits the OER activity. Besides, the smaller grain size owing to Mo doping leads to higher electrochemically active surface area (ECSA) on 4%Mo–Co₃O₄/NC, resulting in its superior bifunctional catalytic activity.     

ZnO/Cu2O-decorated rGO: Heterojunction photoelectrode with improved solar water splitting performance

In present work, we report a facile fabrication process to improve the photoelectrochemical (PEC) performance of ZnO-based photoelectrodes. In order to achieve that, the Cu₂O nanocubes are cathodic-deposited on the as-prepared ZnO nanorods. Then rGO nanosheets are electrodeposited on the ZnO/Cu₂O heterostructures. The fabricated photoelectrodes are systematically studied in detail by different characterization techniques such as powder X-ray diffraction, micro-Raman, X-ray photoelectron spectroscopy, ultraviolet diffused reflectance spectroscopy and photoluminescence spectroscopy analysis. Morphologies of the fabricated photoelectrodes are investigated through electron microscopy in scanning and transmission mode. To evaluate the PEC performance of the fabricated photoelectrodes, the line scan voltammetry (LSV) measurement is performed using a three-electrode system in 0.5-M Na₂SO₄ electrolyte solution under stimulated light illumination at 100 mW/cm² from a 300-W Xenon Arc lamp coupled with an AM 1.5G filter using a three-electrode system. The photocurrent measurement demonstrates that the photoelectrodes based on ZnO/Cu₂O/rGO possess enhanced PEC performance compared to the pristine ZnO and ZnO/Cu₂O photoelectrodes. The photocurrent density of ZnO/Cu₂O/rGO-15 photoelectrode (10.11 mA/cm²) is ∼9 and ∼3 times higher than the photoelectrodes based on pristine ZnO (1.06 mA/cm²) and ZnO/Cu₂O (3.22 mA/cm²). The enhanced PEC performance of ZnO/Cu₂O/rGO photoelectrode is attributed to the excellent light absorption properties of Cu₂O and excellent catalytic and charge transport properties of rGO. Experimental results reveal that the proposed functional nanomaterials have a great potential in water splitting applications.     

Designed synthesis of hierarchical Mn3O4@SnO2/Co3O4 core-shell nanocomposite for efficient electrocatalytic water splitting

The hierarchical Mn₃O₄@SnO₂/Co₃O₄ core-shell nanocomposite has been successfully synthesized via a facile structural construction strategy. The SnO₂/Co₃O₄ nanosheets (SnO₂/Co₃O₄ NSs) were enclosed on the surface of Mn₃O₄ nanorods (Mn₃O₄ NRs). The prepared materials were investigated as the catalyst toward oxygen evolution reaction (OER) performance in alkaline. By contrast, the design of core-shell hierarchical nanocomposite of Mn₃O₄@SnO₂/Co₃O₄ possesses the obvious electrocatalytic OER performance than others, showing the overpotential of approximately 420 mV at a current density of 10 mA cm⁻² with a low Tafel slope of 70.1 mV dec⁻¹, in which the interesting structure can provide the interfacial and cooperative effect between core (hierarchical SnO₂/Co₃O₄ NSs) and shell (1D Mn₃O₄ NRs) that 1D Mn₃O₄ NRs can act as an electron acceptor and accelerates electron transfer, and that hierarchical SnO₂/Co₃O₄ NSs provide a large specific surface area and multiple exposed surface active sites between electrode material and electrolyte.     

Facile synthesis of three-dimensional spherical Ni(OH)2/NiCo2O4 heterojunctions as efficient bifunctional electrocatalysts for water splitting

Synthesis of highly efficient, non-noble and bi-functional electrocatalysts is exceedingly challenging and necessary for water splitting devices. In this work, three-dimensional spherical Ni(OH)₂/NiCo₂O₄ heterojunctions are prepared by a one-step hydrothermal method and the hybrids are explored as efficient electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline electrolyte via tuning different Ni/Co atomic ratios of heterojunctions. The optimized Ni(OH)₂/NiCo₂O₄ (S (1:1)) exhibits high electrocatalytic activity with an ultralow over-potential of 189 mV at 10 mA cm⁻² for the HER. With regard to the OER, the over-potential of the as-synthesized S (1:1) heterojunction is only 224 mV at the current density of 10 mA cm⁻². The improved catalytic performance of the Ni(OH)₂/NiCo₂O₄ heterojunctions is attributed to the chemical synergic combining of Ni(OH)₂ and NiCo₂O₄, large specific surface area for exposing more accessible active sites, and heterointerface for activating the intermediates that facilitates electron/electrolyte transport. The prepared catalyst exhibits good durability and stability in HER and OER catalyzing conditions. This study provides a feasible approach for the building of highly efficient bifunctional water splitting electrocatalysts and stimulates the development of renewable energy conversion and storage devices.     

Facile construction of well-defined hierarchical NiFe2O4/NiFe layered double hydroxides with a built-in electric field for accelerating water splitting at the high current density

Interfacial charge redistribution induced by a strong built-in electric field can expertly optimize the adsorption energy of hydrogen and hydroxide for improving the catalytic activity. Herein, we develop a well-defined hierarchical NiFe₂O₄/NiFe layered double hydroxides (NFO/NiFe LDH) catalysts, exhibiting superior performance due to the strong interfacial electric field interaction between NiFe₂O₄ nanoparticle layers and NiFe LDH nanosheets. In 1 M KOH, NFO/NiFe LDH needs 251 mV and 130 to drive 50 and 10 mA cm^?2 for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Moreover, only 1.517 V cell voltage is needed to reach 10 mA cm^?2 towards overall water splitting. Notably, under simulated industrial electrolysis conditions, NFO/NiFe LDH only needs 289 mV to drive 1000 mA cm^?2. This work puts a deep insight into the role of the built-in electric field in transition metal-based catalysts for accelerating water splitting and scalable industrial electrolysis applications.     

Co-based MOF-derived Co/CoN/Co2P ternary composite embedded in N- and P-doped carbon as bifunctional nanocatalysts for efficient overall water splitting

In this work, we developed ternary metallic cobalt-cobalt nitride-dicobalt phosphide composite embedded in nitrogen and phosphorus co-doped carbon (Co/CoN/Co₂P-NPC) as bifunctional catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The as-prepared Co/CoN/Co₂P-NPC is achieved by simultaneous annealing and phosphating of a Co–N rich metal-organic frameworks (MOFs) precursor. Compare with the phosphorus-free Co/CoN embedded nitrogen-doped carbon electrocatalyst (Co/CoN-NC), the as-prepared Co/CoN/Co₂P-NPC display superior HER and OER low overpotential of 99 mV and 272 mV at current density of 10 mA cm⁻². When Co/CoN/Co₂P-NPC electrocatalyst is use as bifunctional catalysts in overall alkaline water splitting, it exhibit excellent behaviour with 10 mA cm⁻² current at overall cell potential of 1.60 V. The excellent performance of Co/CoN/Co₂P-NPC electrocatalyst is attributed to the phosphating process that could further enhance synergistic effect, create stronger electronic interactions, and form efficient dual heteroatom doping to optimize the interfacial adhesion within the electrocatalyst. This present work will create more opportunities for the development of new, promising and more active sites electrocatalysts for alkaline electrolysis.     

A nano-spherical structure Ni3S2/Ni(OH)2 electrocatalyst prepared by one-step fast electrodeposition for efficient and durable water splitting

Developing non-noble metal catalysts with excellent electrocatalytic performance and stability is of great significance to hydrogen production by water electrolysis, but there are still problems of low activity, complex preparation and high cost. Herein, we fabricated a novel Ni₃S₂/Ni(OH)₂ dual-functional electrocatalyst by a one-step fast electrodeposition on nickel foam (NF). While maintaining the electrocatalytic performance of Ni₃S₂, the existence of heterostructure and Ni(OH)₂ co-catalyst function greatly improves the overall water splitting performance of Ni₃S₂/Ni(OH)₂–NF. Hence, It shows a low overpotential of 66 mV at 10 mA cm^?2 for HER and 249 mV at 20 mA cm^?2 for OER. The dual-functional electrocatalyst needs only 1.58 V at 20 mA cm^?2 when assembled two-electrode electrolytic cell. Impressively, the electrocatalyst also shows outstanding catalytic stability for about 800 h when 20 and 50 mA cm^?2 constant current was applied, respectively which demonstrates a potential electrocatalyst for overall water splitting.     

Electronic regulation and core-shell hybrids engineering of palm-leaf-like NiFe/Co(PO3)2 bifunctional electrocatalyst for efficient overall water splitting

Constructing efficient and stable bifunctional electrocatalysts for overall water splitting remains a challenge because of the sluggish reaction kinetics. Herein, the core-shell hybrids composed of Co(PO₃)₂ nanorod core and NiFe alloy shell in situ grown on nickel foam (NiFe/Co(PO₃)₂@NF) are synthesized. Owing to the hierarchical palm-leaf-like structures and strong adhesion between NiFe alloys, Co(PO₃)₂ and substrates, the catalyst provides a large surface area and rapid charge transfer, which facilitates active sites exposure and conductivity enhancement. The interfacial effect in the NiFe/Co(PO₃)₂ core-shell structure modulates the electronic structure of the active sites around the boundary, thereby boosting the intrinsic activity. Benefiting from the stable structure, the durability of the catalyst is not impaired by the inevitable surface reconfiguration. The NiFe/Co(PO₃)₂@NF electrode presents a low cell voltage of 1.63 V to achieve 10 mA cm^?2 and manifests durability for up to 36 h at different current densities.     

Facile construction of heterostructural Ni3(NO3)2(OH)4/CeO2 bifunctional catalysts for boosted overall water splitting

Interface engineering has aroused vitally widespread concern since it could be an effective strategy for exploring high-performance and low-cost water oxidation electrocatalysts. Herein, we report a hetero-structured Ni₃(NO₃)₂(OH)₄/CeO₂/NF (NNO/CeO₂/NF) electrode, exhibiting superior performance owning to the NO₃^? anion substitution for the OH^? in nickel hydroxide to form Ni₃(NO₃)₂(OH)₄, together with its interface synergy with ceria. In alkaline solution, the NNO/CeO₂/NF electrocatalyst could catalyze the OER with an overpotential of 330 mV to approach 50 mA cm^?2. Also, it needs only an overpotential of 120 mV to reach 10 mA cm^?2 for HER. Additionally, when a standard two-electrode water electrolyzer is fabricated by employing NNO/CeO₂/NF as both the cathode and anode, it can generate 10 mA cm^?2 at 1.64 V and operate steadily without performance degradation after 25 h. This research provides a novel perspective for reasonable design of advanced catalytic materials with improvements in the field of electrocatalysis.     

Hydrogen production via highly efficient electrocatalyst based on 3D NixCo1-x(OH)2/NiFe-AM induce overall water splitting

The main factors limiting water splitting producing hydrogen production are overpotential, activity and persistence of electrocatalysts. Herein, a novel Ni_xCo_1-x(OH)₂ coupled with NiFe amorphous compound array growing on nickel foam substrate (expressed as Ni_xCo_1-x(OH)₂/NiFe-AM) was developed by facile hydrothermal and electrodeposition methods. Significantly, Ni_xCo_1-x(OH)₂/NiFe-AM with this unique structural exhibits superior activity and stability in the two half reactions of water electrolysis. In addition, when tested in an alkaline electrolyte with a current density of 10 mA cm⁻², the overpotentials of HER and OER was 157 mV and 196 mV (60 mA cm⁻²), respectively. The stability can up to 60 h. These test results show through constructing hierarchical nano-thron architecture enhanced electrocatalytic activity to produce hydrogen and oxygen.     

N,S co-doped NiCo2O4@CoMoO4/NF hierarchical heterostructure as an efficient bifunctional electrocatalyst for overall water splitting

Electrocatalytic overall water splitting technology has received considerable attention in recent years. The fabrication of low-cost, earth-rich and potent bifunctional electrocatalysts is vital for hydrogen evolution (HER) and oxygen evolution reactions (OER). Herein, the N and S co-doped NiCo₂O₄@CoMoO₄ heterostructures (N, S–NCO@CMO₄₀₀) are fabricated by CVD and hydrothermal methods. N and S atoms as auxiliary active centers can increase the activity of Ni, Co and Mo atoms at the same time. Hierarchical heterostructures generate more interfaces to accelerate mass transfer and enlarge the electrochemical surface area, which greatly enhances the catalytic activity. The catalyst displays outstanding OER performance. The overpotentials of OER and HER are 165 and 100 mV at a current density of 10 mA cm^?2, respectively. More importantly, the N, S–NCO@CMO₄₀₀-based water splitting cell has a low voltage of 1.46 V at 10 mA cm^?2. Furthermore, the N, S–NCO@CMO₄₀₀ runs for 120 h in stable operation. This work provides new ideas for the design of hierarchical heterostructures with two-element incorporation.     

Origin of the overall water splitting activity over Rh/Cr2O3@ anatase TiO2 following UV-pretreatment

Anatase TiO₂ has long been known to be one of the best photocatalysts. Its conduction band potential is thermodynamically allowed to drive a diverse range of photooxidation reactions. However, anatase TiO₂ cannot oxidize water into oxygen in photocatalytic overall water splitting that involves multi-hole transfers. In the present study, a simple pretreatment of anatase TiO₂ with highly-intense UV irradiation is demonstrated to enable overall water splitting upon loading with a Rh/Cr₂O₃ cocatalyst. Based on light-induced infrared absorption spectroscopy and time-resolved microwave conductivity, it is suggested that the efficient removal of deep hole traps permits free holes to possess a sufficiently strong oxidizing potential for water oxidation over Rh/Cr₂O₃@TiO₂.