MgO as promoter for electrocatalytic activities of Co3O4–MgO composite via abundant oxygen vacancies and Co2+ ions towards oxygen evolution reaction

Oxygen evolution reaction (OER) is known as bottleneck problem during the water splitting process due to high energy barrier and non-availability of efficient nonprecious electrocatalysts. The cobalt oxide (Co₃O₄) in the spinel phase has limited OER activity and stability in the alkaline media. For this purpose, we have carried out the synthesis of Co₃O₄–MgO (CM) composite by wet chemical method and it offers abundant oxygen vacancies and Co²⁺ concentration for the efficient OER reaction. The effect of different amounts of MgO on the OER activity of Co₃O₄ was also studied. Despite inactivity of MgO towards OER, it creates high density of oxygen vacancies and favored the formation Co²⁺ ions at the surface, thus accelerated the OER kinetics. The physical studies were performed to investigate the morphology, crystalline structure, surface information and chemical composition using several analytical techniques. The optimized CM-0.1 composite produced an overpotential of 274 mV at 10 mAcm⁻² which is lower in value than the pristine Co₃O₄. The significant enhancement in the OER activity was verified by the large value of electrochemical active surface area values 12.8 μFcm⁻² and the low charge transfer resistance of 45.96 Ω for the optimized CM-0.1 composite. The use of abundance materials for the synthesis of CM composite revealed an enhanced OER performance, suggesting the dynamic role of MgO, therefore it could be used for improving the electrochemical properties of extended range of metal oxides for specific application especially energy conversion and storage devices.     

Fabrication of 3-D ZnO/CN nanorods for photo-/electrocatalytic water splitting: An efficient morphology for charge carriers transportation

The present study is about the fabrication of an efficient photo-/electrocatalyst, prepared via in-situ hydrothermal coupling of ZnO with g-C₃N₄. The results prove this electrocatalyst as suitable band structure semiconductor. The crystalline nature and related morphological parameters are controlled by optimized hydrothermal and calcination temperatures conditions. A series of physicochemical characterization are applied to inquire the crystalline structure, surface morphology, optical capabilities and charge transportation properties. Results revealed that the sample acts as excellent electrocatalyst with OER current density at 10 mAcm⁻² @ 335 mV and the HER at 100 mAcm⁻² @ −225 mV. While upon illuminations its catalytic properties further enhance at OER 10 mAcm⁻² @ 326 mV and for HER current density of 100 mAcm⁻² @ −167 mV. It can be seen from the present study that g-C₃N₄ play gigantic role in enhancing the catalytic property of ZnO and hence it leads to a relationship between hierarchical features and photo-/electrochemical activity for water splitting.     

An efficient and durable bifunctional electrocatalyst based on PdO and Co2FeO4 for HER and OER

The adoption of effective, minimal, and versatile electrocatalysts for water splitting to generate hydrogen fuels is of critical importance. The bulk of newly described materials have considerable onset potential, but their electrocatalytic activity is limited by weak electrical conductivity and a limited range of catalytic sites. The combination of a few precious metals added with transition metal-based compounds is a novel and captivating approach. Herein, cobalt ferrite oxide (Co₂FeO₄) @ palladium oxide (PdO) nanostructures have been prepared through the combined use of hydrothermal and ultraviolet (UV) irradiation techniques. For hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) kinetics, the modified composition offers a high concentration of active sites, improved electrical conductivity, and stability. The Co, Fe, and Pd ions at the composite system's interface may affect the adsorption energy of reaction intermediates synergistically, enabling the process to continue with less potential. The electrocatalyst Co₂FeO₄@PdO demonstrates an excellent bifunctional approach to electrochemical water splitting (EWS) for HER and OER in alkaline medium. As-prepared electrocatalyst shows an overpotential value of 269 and 259 mV for HER and OER at 10 and 20 mA/cm² current densities respectively. The low charge transfer resistance values such as 72.2 and 62.4 Ω and durability for 48 h has been observed toward HER and OER, support this material as an efficient and durable electrocatalyst for energy conversion systems.     

Thin-film iron-oxide nanobeads as bifunctional electrocatalyst for high activity overall water splitting

Developing only Fe derived bifunctional overall water splitting electrocatalyst both for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) while performing at low onset overpotential and with high catalytic stability is a rare instance. We present here the first demonstration of unique iron-oxide nanobeads (FeO_x-NBs) based electrocatalyst executing both OER and HER with high activity. Thin-film electrocatalytic FeO_x-NBs assembly is surface grown via simple spray coating (SC). The unique SC/FeO_x-NBs propels OER initiating water oxidation just at 1.49 V_RHE (η = 260 mV) that is the lowest observable onset potential for OER on simple Fe-oxide based catalytic films reported so far. Catalyst also reveals decently high HER activity and competent overall water splitting performance in the FeO_x-NBs two-electrode system as well. Catalyst also presents stable kinetics, with promising high electrochemically active surface area (ECSA) of 1765 cm², notable Tafel slopes of just 54 mV dec^1? (OER) and 85 mV dec^1? (HER), high exchange current density of 1.10 mA cm^2? (OER), 0.58 mA cm^2? (HER) and TOF of 74.29s^1?@1.58V_RHE, 262s^1?@1.62V_RHE (OER) and 82.5s^1?@-0.45V_RHE, 681s^1?@-0.56V_RHE (HER).     

One-step solution-induced impregnation synthesis of strongly coupled platinum–molybdenum/silicon carbide quantum dots heterostructures encapsulated on reduced graphene oxide sheet as electrocatalyst for hydrogen evolution reaction

Strongly coupled platinum-based transition-metal oxide/carbon hybrids and the development of quantum-dot structures of hybrid catalysts are cost-effective and maximize accessible active sites. However, a significant obstacle still exists for the rational proposal and simple synthesis of hybrid quantum-dot material catalysts. Herein, novel Pt_xMo_1-xSiC quantum dots encapsulated in reduced graphene oxide (rGO) (Pt_xMo_1-xSiC QDs @rGO) for catalyzing the hydrogen evolution reaction (HER) were fabricated through a simple solution-induced impregnation method. The optimized Pt₅Mo₉₅SiC QDs @rGO catalyst only require overpotentials of 18 mV and 25 mV to deliver current densities of 10 mA cm⁻² and 250 mA cm⁻² in acidic media, respectively. The synergistic effects of the inner Pt_xMo_1-xSiC QDs networks and outer conductive rGO sheets that promote electron transfer are responsible for the outstanding HER performance. This work presents a novel method for producing an extremely effective HER catalyst for applications on large-scale.     

Efficient electrochemical hydrogen evolution reaction and solar activity via bi-functional GO/Co3O4–TiO2 nano hybrid structure

Highly proficient electro and solar catalyst of mixed metal oxides Co₃O₄–TiO₂ modified with graphene oxide (GO) have been synthesized by simple and cost-effective way using sol-gel methodology. This catalyst demonstrated versatile bi-functional features towards the hydrogen evolution reaction (HER) in catalytic water splitting along with solar photo catalytic activity in the degradation of Methyl Orange (MO). XRD profile confirmed that composite presented an anatase and cubic phase for TiO₂ and Co₃O₄, respectively, with the GO network. The morphological structures confirm flaky texture of Co₃O₄ with small irregular spheres of TiO₂ nanoparticles randomly dispersed on the broken sheets of GO. GO and clusters of Co²⁺/Co³⁺ in different regions of host TiO₂ are accountable for decreasing band gap in the composite samples. Co–O–Ti and Co–Ti–C linkages in the composite materials are confirmed by Raman and FTIR studies. In electro catalytic HER in alkaline medium GO/Co₃O₄–TiO₂ catalyst illustrated low onset potential ~343 mV vs. RHE, high current density ~43 mA cm⁻² corresponding small Tafel slope ~97 mV/dec and small R_ct as compared to other catalysts. For HER in GO/Co₃O₄–TiO₂, Co²⁺ sites are more catalytically active than Co³⁺ sites along with Ti⁴⁺ and GO provides the more active surface area by reducing the agglomeration between the mixed metal oxides. GO/Co₃O₄–TiO₂ shows the highest photo catalytic performance over MO as compared to binary and ternary composites. Pining of metal oxides with reactive oxygen functional moieties of GO considerably improve the photo catalytic degradation activity and helpful in the separation of charge carriers for HER.     

Pronounced effect of phosphidization on the performance of CoOx encapsulated N-doped carbon nanotubes towards oxygen evolution reaction

Research on water splitting reaction is on priority to explore an alternative source of energy with little to no carbon emissions. Among the two half reactions of electrochemical water splitting, oxygen evolution reaction (OER) is highly desirable yet challenging to prepare a cost effective and viable electrocatalyst to boost the OER activity. Herein, we have prepared a novel electrocatalyst, CoO_x-CoP/N-CNTs, by the phosphidization of cobalt oxides (CoO_x) encapsulated N- doped carbon nanotubes (CoO_x/N-CNTs). The CoO_x/N-CNTs composite is derived via pyrolysis of cobalt based zeolitic imidazole framework (ZIF-12) at 950 °C under argon atmosphere. The CoO_x/N-CNTs is phosphidized at various temperatures ranging from 320 °C to 400 °C. The optimized temperature to attain the best catalytic activity is 380 °C. The phosphatized material, CoO_x-CoP/N-CNTs, shows superior performance towards OER with an overpotential of 250 mV @ 20 mAcm^?2 vs 532 mV @ 20 mAcm^?2 of un-phosphidized material, CoO_x/N-CNTs, which shows significant effect of phosphidization. The maximum current density of 160 mAcm^?2 in 1 M KOH solution is achieved.     

Dysprosium doped copper oxide (Cu1-xDyxO) nanoparticles enabled bifunctional electrode for overall water splitting

The production of hydrogen, a favourable alternative to an unsustainable fossil fuel remains as a significant hurdle with the pertaining challenge in the design of proficient, highly productive and sustainable electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, the dysprosium (Dy) doped copper oxide (Cu_1-xDy_xO) nanoparticles were synthesized via solution combustion technique and utilized as a non-noble metal based bi-functional electrocatalyst for overall water splitting. Due to the improved surface to volume ratio and conductivity, the optimized Cu_1-xDy_xO (x = 0.01, 0.02) electrocatalysts exhibited impressive HER and OER performance respectively in 1 M KOH delivering a current density of 10 mAcm^?2 at a potential of ?0.18 V vs RHE for HER and 1.53 V vs RHE for OER. Moreover, the Dy doped CuO electrocatalyst used as a bi-functional catalyst for overall water splitting achieved a potential of 1.56 V at a current density 10 mAcm^?2 and relatively high current density of 66 mAcm^?2 at a peak potential of 2 V. A long term stability of 24 h was achieved for a cell voltage of 2.2 V at a constant current density of 30 mAcm^?2 with only 10% of the initial current loss. This showcases the accumulative opportunity of dysprosium as a dopant in CuO nanoparticles for fabricating a highly effective and low-cost bi-functional electrocatalyst for overall water splitting.     

Synergistic coupling of CoFe-layered double hydroxide nanosheet arrays with reduced graphene oxide modified Ni foam for highly efficient oxygen evolution reaction and hydrogen evolution reaction

Novel CoFe-LDH (layered double hydroxide) nanosheet arrays in situ grown on rGO (reduced graphene oxide) uniformly modified Ni foam were synthesized by a citric acid-assisted aqueous phase coprecipitation strategy. Systematic characterizations indicates that the series of Co_xFe₁-LDH/rGO/NF (x = 4, 3, 2) all show Co_xFe₁-LDH nanosheets (150–180 × 15 nm) grown vertically on the surface of rGO/NF. Especially, the Co₃Fe₁-LDH/rGO/NF exhibits the best performance with overpotentials of 250 and 110 mV at 10 mA cm^?2 in 1 M KOH for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), respectively. When it is used as cathode and anode simultaneously for overall water splitting, they require 1.65 and 1.84 V at 10 and 100 mA cm^?2, respectively. Excellent performance of Co₃Fe₁-LDH/rGO/NF is due to the nanosheet arrays structure with open channels, synergistic coupling between Co₃Fe₁-LDH and rGO enhancing electrical conductivity, and in-situ growth of Co₃Fe₁-LDH on rGO/NF enhancing stability.     

NiCo2O4 nanostructures loaded onto pencil graphite rod: An advanced composite material for oxygen evolution reaction

Driving oxygen evolution reaction (OER) at extremely low overpotential and the blockage of oxygen gas inside the catalytic material leads to the deactivation of catalytic activity, therefore it is an essential step in electrochemical energy conversion systems, but still very challenging task. The clay minerals including bentonite and kaolinite are rich with plenty of active centers and favorable chemical composition for the catalysis applications but limited by the insulating properties, thus they cannot be used as an electrode material for the water splitting. The unique presence of clay minerals in the form of pencil graphite rod (PGR) and its attractive architecture enabled us to exploit advantageous features and use them as an in situ electrode for growth of metal oxide nanostructures for the electrolysis applications. The naturally inherent presence of SiO₂ favors the catalytic properties and durability of the electrode whereas the MgO produces the abundant oxygen vacancies and Co³⁺ ions for OER process. Herein, we present a facile approach of using PGR as host substrate and co-catalyst for the loading of Co₃O₄, NiCo₂O₄ and NiO nanostructures and the modified electrode carried high porosity for easily bubbling of oxygen gas, plenty of intrinsic active centers coming from both clay minerals and metal oxides for excellent OER process. The fabricated electrode is physically well-characterized, and it has a natural ability to sustain a long term stability even at higher current densities and industrial electrolyzer conditions. The NiCo₂O₄/PGR, Co₃O₄/PGR, and NiO/PGR electrodes exhibit an overpotential of 234, 242 and 272 mV respectively at a current density of 100 mAcm^?2 in 1.0 M KOH electrolytic solution. The presence of large number of oxygen vacancies through SiO₂ and MgO, high Ni²⁺/Ni³⁺ and Co³⁺/Co²⁺ ratios, multi metal centers, large specific surface area, high pore volume, high electrochemical active surface area and fast charge transport within the NiCo₂O₄/PGR are the main reasons for its superfast OER kinetics. Thus, the proposed method of electrode design will pave a potential way for high performance electrochemical devices like metal air batteries, fuel cell and supercapacitors.     

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.     

Se-doped cobalt oxide nanoparticle as highly-efficient electrocatalyst for oxygen evolution reaction

Electrolysis of water has been one of the most promising approaches for renewable energy resources while the efficient oxygen evolution reaction (OER) remains challenging. Herein, a series of different ratio of Se doped Co₃O₄ nanoparticles XSe-Co₃O₄ are prepared by hydrothermal method and applied as OER electrocatalysts. Se^2? is doped into the Co₃O₄ crystal lattice by substituting of O^2? and a large number of oxygen vacancies are generated, which provides more available activity sites for OER. Se doping increases the surface ratio of Co²⁺/Co³⁺ and accelerates the electron transport that favors OER activity promotion. The optimized doping ratio of 6%Se–Co₃O₄ presents low overpotential of 281 mV at 10 mA cm^?2, as well as a low Tafel slope of 70 mV dec^?1 in 1 M KOH solution, which has great advantages compared to the recently reported Co₃O₄-based OER electrocatalysts. This work provides new ideas for the development of efficient Co₃O₄-based OER electrocatalysts.     

Reduced CoFe2O4/graphene composite with rich oxygen vacancies as a high efficient electrocatalyst for oxygen evolution reaction

Oxygen evolution reaction (OER) is regarded as a limit-efficiency process in electrochemical water splitting generally, which needs to develop the effective and low-cost non-noble metal electrocatalysts. Oxygen vacancies have been verified to be beneficial to enhance the electrocatalytic performance of catalysts. Herein, we report the facile synthesis of reduced CoFe₂O₄/graphene (r-CFO/rGO) composite with rich oxygen vacancies by a citric acid assisted sol-gel method, heat treatment process and the sodium borohydride (NaBH₄) reduction. The introduction of graphene and freezing dry technique prevents the restacking of GO and the aggregation of CFO nanoparticles (NPs) and increases the electronic conductivity of the catalyst. Fast heating rate and low anneal temperature favors to obtain low crystallinity and lattice defects for CFO. NaBH₄ reduction treatment further creates the rich oxygen vacancies and electrocatalytic active sites. The obtained r-CFO/rGO with high specific surface area (108 m² g⁻¹), low crystallinity and rich oxygen vacancies demonstrates a superior electrocatalytic activity with the smaller Tafel slope (68 mV dec⁻¹), lower overpotential (300 mV) at the current density of 10 mA cm⁻², and higher durability compared with the commercial RuO₂ catalyst. This green, low-cost method can be extended to fabricate similar composites with rich defects for wide applications.     

Synthesis of nickel hydroxide/reduced graphene oxide composite thin films for water splitting application

Facile synthesis of highly efficient and low-cost electrocatalyst for oxygen evolution reaction (OER) is important for large-scale hydrogen production. Herein, nickel hydroxide/reduced graphene oxide (Ni(OH)₂/rGO) composite thin film was fabricated using dip-coating followed by electrodeposition method on Ni foam substrate at room temperature. The deposited composite film shows amorphous nature with ultra-thin Ni(OH)₂ nanosheets vertically coated on rGO surface, which provides large electrochemical surface area and abundant catalytically active sites. It exhibits a low overpotential of 260 mV @10 mA cm⁻² as compared to the pristine electrodes and excellent long-term stability up to 20 hours in 1 M KOH solution. The electrochemical active surface area and Tafel slope of the composite electrode are 20.2 mF cm⁻² and 35 mV dec⁻¹, respectively. The superior water oxidation performance is a result of high catalytically active sites and improved conductivity of the composite electrode.     

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.     

Highly efficient and stable bifunctional electrocatalyst for water splitting on Fe–Co3O4/carbon nanotubes

Replacement of precious platinum (Pt) or ruthenium oxide (RuO₂) catalysts with efficient, cheap and durable electrocatalysts from earth-abundant elements bifunctional alternatives would be significantly beneficial for key renewable energy technologies including overall water splitting and hydrogen fuel cells. Despite tremendous efforts, developing bifunctional catalysts with high activity at low cost still remain a great challenge. Here, we report a nanomaterial consisting of core-shell-shaped Fe–Co₃O₄ grown on carbon nanotubes (Fe–Co₃O₄/CNTs) and employed as a bifunctional catalyst for the simultaneous electrocatalysts on oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The Fe–Co₃O₄/CNTs electrocatalyst outperforms the commercial RuO₂ catalyst in activity and stability for OER and approaches the performance of Pt/C for HER. Particularly, it shows superior electrocatalytic activity with lowering overpotentials of 120 mV at 10 mA cm^?2 for HER and of 300 mV at 10 mA cm^?2 for OER in 1 M KOH solution. The superior catalytic activity arises from unique core-shell structure of Fe–Co₃O₄ and the synergetic chemical coupling effects between Fe–Co₃O₄ and CNTs.     

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.     

Co3O4 nanosheet arrays treated by defect engineering for enhanced electrocatalytic water oxidation

Due to its poor electrical conductivity and finite exposed active sites, the development of high activity Co₃O₄ oxygen evolution reaction (OER) electrocatalysts remains a major challenge. Oxygen vacancies can enhance the electrical conductivity of electrocatalysts and reduce the adsorption energy of H₂O molecules on surfaces, thereby significantly enhancing their electrocatalytic activity. Taking inspiration from this, we demonstrate a green and facile reduction strategy to prepare reduced Co₃O₄ nanosheet arrays (R-Co₃O₄ NSA) with large electrochemical surface area and rich in surface oxygen vacancies. Compared to pristine Co₃O₄ nanosheet arrays (P-Co₃O₄ NSA), R-Co₃O₄ NSA exhibits better OER performance, with a lower overpotential of 330 mV at a current density of 20 mA cm^?2 and a smaller Tafel slope of 72 mV dec^?1. Impressively, the excellent properties of R-Co₃O₄ NSA can rival to the state-of-the-art noble metal oxide electrocatalyst (IrO₂). This strategy of defect-engineering offers a briefness and cost-effective means for the development of highly efficient OER systems.     

Three-dimensional reduced graphene oxide–Mn3O4 nanosheet hybrid decorated with palladium nanoparticles for highly efficient hydrogen evolution

A three-dimensional (3D) reduced graphene oxide–Mn₃O₄ nanosheet (Mn₃O₄@rGO) hybrid was achieved by simple electrodeposition technique. Small palladium nanoparticle were homogeneously anchored onto Mn₃O₄@rGO substrate through the reduction of palladium salt. The interpenetrating network architecture of Mn₃O₄@rGO greatly inhibited the aggregation of 2D sheets of Mn₃O₄ and rGO, and the open 3D orientation of the Mn₃O₄@rGO hybrid nanosheets on the electrode facilitated both mass transport and electron transfer as well as maximally exposed active sites. The introduction of Mn₃O₄ enhanced the structural and electrochemical stability of rGO. The as-synthesized Pd/Mn₃O₄@rGO hybrid was employed as an electrocatalyst for electrocatalytic hydrogen evolution reaction (HER). The electrocatalyst showed a low overpotential of 20 mV at 10 mA cm^?2, a small Tafel slope of 48.2 mV dec^?1, and a large exchange current density of 0.59 mA cm^?2. Importantly, the catalyst possessed superior durability with 85.87% of catalytic activity after a long-time test (10 h). This work presents a simple and efficient stratagy to construct high-performance electrocatalysts for energy and environmental applications.     

Design of Ni/NiO–TiO2/rGO nanocomposites on carbon cloth conductors via PECVD for electrocatalytic water splitting

The facile synthesis and design of noble metal-free efficient catalysts to accelerate the sluggish kinetics of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is still a big challenge for electrolytic water splitting. In that context, the preparation of efficient catalysts with superior catalytic activity from cheap raw materials on a large scale is crucial. Briefly, Ni/NiO/TiO₂/rGO is designed using the environmental-friendly and easily up-scalable PECVD technique. This trinary composite presents significance in regulating the crystalline structure, composition and electronic properties towards superior HER and OER activity in acidic solution as bifunctional electrocatalysts for efficient water splitting. Together with the promising long-term stability and durability, Ni/NiO/TiO₂/rGO displays excellent electrocatalytic activity towards HER with η₁₀ of 130 mv vs RHE and a Tafel slope of 40 mV/dec.