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In this work, we have successfully synthesized the cost-effective, abundant in nature and environmentally friendly SrMoO 4 /MWCNT-PVP by using the co-precipitation technique for hydrogen evolution reaction (HER). Prepared nanocomposites were characterized by XRD, which confirms the formation of tetragonal structure of SrMoO 4 and indexed with JCPDS (01-074-3912). Raman spectra confirm the combination of SrMoO 4 with carbon composite (verified by D and G band 1.02 I D /I G ratio) and its functional group was further analyzed with the help of FTIR spectra. Synthesized product morphology was characterized by using SEM and TEM images, which confirms formation of well-defined dumb-bell shaped nanostructures with the combination of carbon nanotube and also it further confirms the formation of polycrystalline nature of the material. The elemental composition was analyzed by EDS images, which confirms the occurrence of Sr, Mo, O, and C in an appropriate form with a uniform distribution, respectively. MWCNT in SrMoO 4 incorporation led to decrease overpotential of 204 mV and 110 mV/dec Tafel slope of the material, which was examined by the LSV curves and Tafel plot analysis. Electrochemical impedance spectroscopy was also investigated, and it delivered the small charge-transfer resistance of 248 Ω, which further supporting the HER analysis and denoting the promising HER kinetics. Therefore, our work unlocks a new path for the properly tuned nanostructured morphology of metal oxide with carbon composite for electrochemical hydrogen evolution reaction application. [ABSTRACT FROM AUTHOR]

Designing an ideal bi-functional electrocatalyst for the overall water splitting plays significant function in alternative energy construction. Based on the previous literatures, the Co 3 O 4 /g-C 3 N 4 nanocomposite has been investigated as the bi-functional electrocatalyst. In the present study, the facile hydrothermal route was approached to synthesize the Co 3 O 4 /g-C 3 N 4 nanocomposite to enhance the electrocatalytic activity towards oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Further, Co 3 O 4 /g-C 3 N 4 electrochemical analysis was undergone in an aqueous alkaline solution of 1 M potassium hydroxide for both OER and HER. High electrocatalytic nature of prepared Co 3 O 4 /g-C 3 N 4 nanocomposite delivered the low 170 mV overpotential value and 151 mV at 20 mA/cm2 with Tafel values 188 mV/dec and 176 mV/dec for OER and HER. Also electrochemical surface area (ECSA) of prepared Co 3 O 4 /g-C 3 N 4 nanocomposite was estimated from double layer capacitance (C dl) values, and calculated ECSA values are 0.027 cm2 and 0.097 cm2 for OER and HER respectively. The resultant Co 3 O 4 /g-C 3 N 4 nanocomposite reached the low charge transfer resistance value of 15.9 Ω for OER and 22.7 Ω for HER which could acts as strong parameter to improve conductivity of the prepared electrode for both half reactions. Along with that, stability of Co 3 O 4 /g-C 3 N 4 nanocomposite exhibits the outstanding performance at the current density of 10 mA/cm2 with only minimum amount of loss even after 16 h for both OER and HER. Hence, the synthesized Co 3 O 4 /g-C 3 N 4 nanocomposite was act as an optimistic choice of the bi-functional electro catalyst for sustainable energy production. • Attempted Co 3 O 4 /g-C 3 N 4 for bi-functional electrochemical water splitting. • Co 3 O 4 /g-C 3 N 4 delivered 170 and 151 mV at 20 mA/cm2 with low Tafel values 188 and 176 mV/dec for OER and HER. • Stability of Co 3 O 4 /g-C 3 N 4 for long duration up to 16 h results 74% and 60% retention for both OER and HER. • Co 3 O 4 /g-C 3 N 4 was optimistic choice of the bi-functional electrocatalyst. [ABSTRACT FROM AUTHOR]

Herein, bimetal (Mn, Co) codoping on a CuO host is aimed at enhancing oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) activity. Codoping of Mn and Co on CuO to enhance bifunctional action in electrochemical water splitting has not yet been investigated to the best of our knowledge. Literatures are focused on unary Mn-doped CuO or Co-doped CuO nanostructures. Mn, Co codoped CuO through an easy chemical coprecipitation method has been successfully attempted and is more beneficial which is the novelty of the present work. Defect-enriched ample active sites (Mn2+/Mn3+ and Co2+/Co3+) along with Cu2+ in the host CuO achieved high current density (100 mA/cm2) in OER and HER with low overpotential such as 468 mV and 271 mV, respectively. Faster charge transfer and diffusion ability was stimulated by the bimetal codoping CuO. Reasonable Tafel plot values (OER: 199 mV/dec, and HER: 21 mV/dec) with improved water-splitting reaction kinetics were achieved for the Mn, Co codoped CuO nanoflakes. The double-layer capacitance ( C dl ) value of 27.5 mF/cm2 for Mn, Co codoped CuO nanoflakes was achieved. Similarly, the increasing order of an electrochemically active surface area (EASA) was exhibited by the consequent addition of bimetal doping on CuO, denoted as Mn , Co / CuO > Co / CuO > Mn / CuO > CuO. The evidence shows that the codoping strategy could facilitate rapid reaction kinetics to develop overall water splitting. The charge transfer resistances ( R ct ) of 3.6 Ω and 1.2 Ω for the Mn, Co codoped CuO nanostructure corresponding to the OER and HER, respectively, were reported. The long-term stability over 16 h with negligible loss was reported for both the OER and the HER performance. Thus, this work contributes to better insight and analysis of the successful codoping of bimetal elements in earth-abundant electrocatalysts to enhance and make practical the electrocatalytic water-splitting activity. [ABSTRACT FROM AUTHOR]

Nowadays, electrochemical water splitting is a securing alternative for clean-energy production and also an efficient expertise for oxygen and hydrogen production. Compared to single metal-based electrocatalyst, multi metal-based electrocatalyst offers more active sites, high surface area, and distinctive nanostructure for effective water oxidation. In this work, nickel and cobalt co-doped MnCO 3 was successfully synthesized via a facile co-precipitation technique. Rhombohedral crystal phase of MnCO 3 nanostructures and its crystallite sizes were thoroughly analyzed by the XRD spectra. Incorporation of doping element such as Ni and Co in MnCO 3 nanostructures exhibited two different morphologies which enhanced the catalytic performance of the prepared samples. Large surface area and porosity of the nanomaterials improved the stability and activity of the prepared MnCO 3 nanostructures. EDX analysis confirmed Mn, C, O, Ni and Co elements in stoichometric ratio. Moreover, the specific capacitance of (Ni, Co) co-doped MnCO 3 nanostructures attained 581 F/g while the other electrodes attained only 207, 332 and 175 F/g respectively. A small Tafel slope with low overpotential of Ni, Co co-doped MnCO 3 nanostructures was 20.2 mV/dec and 293 mV respectively. Therefore, the prepared electrocatalysts of Ni, Co co-doped MnCO 3 nanostructure is one of the attractive anode material for high performance energy conversion applications. • Ni, Co co-doped MnCO 3 attained 581 F/g while others attained 207, 332 and 175 F/g. • Ni, Co co-doped MnCO 3 explored low 293 mV overpotential. • Ni, Co co-doped MnCO 3 is attractive anode for high performance energy conversion. [ABSTRACT FROM AUTHOR]

Hydrogen is one of the popular abundant elements in the world and, it is rising as a preferential energy and has developed a tool for decarbonization. Recently, hydrogen has been considered as next generation fuel for cars, trucks, homes, etc, because of the arising of worse climate. In this present work, the cost-effective and efficient electrocatalyst of calcium molybdate nanostructures were successfully prepared with the help of non-ionic surfactant (PEG) through the co-precipitation method for hydrogen evolution reaction. In XRD spectra, the high crystallite peak observed at 28.4° value corresponded to (112) lattice planes confirmed the formation of calcium molybdate nanostructures. In Raman spectra, the existence of tetrahedral [MoO 4 ] clusters and octahedral [CaO 8 ] clusters confirmed tetragonal calcium molybdate nanostructures formation. In SEM analysis, unique morphologies such as dumbbell and spindle-like structures was observed, which was achieved by using the PEG. The pore volume, pore diameter and specific surface area of CaMoO4–6 ml PEG were found to be 0.149 cc/g, 11.685 nm and 28.07 m2/g respectively. Electrochemical performance confirmed that the CaMoO4–6 ml PEG nanostructures exhibited superior HER activity with the low 198 mV overpotential at 10 mA/cm2 and lesser 204 mV/dec Tafel slope value. The charge transfer resistance of CaMoO4–6 ml PEG was 0.65 Ω, which has smaller than that of other electrocatalysts such as pure CaMoO4 (24.9 Ω), CaMoO4–2 ml PEG (2.47 Ω) and CaMoO4–4 ml PEG (2.04 Ω). The excellent HER activity was explored elevated electronic conductivity, mesoporous nature, high surface area and, unique morphology. [Display omitted] • CaMoO4–6 ml PEG explored 0.149 cc/g, 11.685 nm pore volume and diameter, 28.07 m2/g surface area. • CaMoO4–6 ml PEG exhibited superior HER activity with 198 mV at 10 mA/cm2 and lesser Tafel slope value of 204 mV/dec. • Excellent HER activity attributed high electronic conductivity, mesoporous nature, large surface area and, unique morphology. [ABSTRACT FROM AUTHOR]

[Display omitted] • Gd-CeO 2 exhibited low overpotential of 99 mV for HER and 369 mV for OER. • Gd-CeO 2 exhibited small Tafel slope 211 mV/dec for HER and 183 mV/dec for OER. • 2% Gd doped CeO 2 exhibited outstanding stability of 70% retention. Hydrogen evolution reaction (HER) is a significant half reaction in water splitting and it is spirit of energy storage and conversion applications. Recently, high durability and catalytic activity of effective electrodes are necessary to enlarge clean and sustainable energy sources. However, overcoming the overpotential and to improve HER and OER performance is still one of the complicated tasks. Hence, in this present work, gadolinium (Gd) doped cerium oxide (CeO 2) was successfully synthesized through a facile co-precipitation method. High intense peak at 28.5° clearly indicated CeO 2 cubic structure formation identified by using X-Ray diffraction. The optical phonon mode of F 2g and oxygen vacancies mode was detected by using Raman spectra. The optical properties of CeO 2 were detected with help of photoluminescence spectroscopy (PL). Fourier-transform infrared (FTIR) spectroscopy confirmed Ce-O vibration of CeO 2 crystal existence. Surface morphology of CeO 2 was thoroughly studied by using SEM images. HER and OER activity of pristine and Gd doped CeO 2 was thoroughly investigated with the help of linear sweep voltammetry. Compared to pristine CeO 2 , high content of Gd doped CeO 2 exhibited excellent HER and OER activity with low overpotential (99 mV for HER and 369 mV for OER) and small Tafel slope (211 mV/dec for HER and 183 mV/dec for OER). Addition of rare earth metal influenced the structural and catalytic properties of optimized metal oxide. Hence, the incorporation of Gadolinium in CeO 2 plays a crucial role to enhance both HER and OER performance and it is one of the good candidates for energy conversion applications. [ABSTRACT FROM AUTHOR]

• Orthorhombic SrV 2 O 6 was confirmed employing X-Ray diffraction. • 0.01 M citric acid assisted SrV 2 O 6 explored 29.11 m2/g high surface area. • 0.01 M CA-SrV 2 O 6 exhibited 78 and 337 mV to deliver 10 and 100 mA/cm2. • It displays better catalytic performance with low 83.3 mV/dec Tafel slope. A novel strontium vanadate for electrochemical hydrogen evolution reaction was reported. SrV 2 O 6 orthorhombic phase was confirmed employing X-Ray diffraction with 34, 29 and 34 nm crystallite size of pristine, 0.01 and 0.02 M citric acid assisted SrV 2 O 6. 0.01 M citric acid assisted SrV 2 O 6 high BET surface area was 29.11 m2/g. Electrochemical HER performance revealed that low concentration of citric acid assisted SrV 2 O 6 nanostructure exhibited 78 and 337 mV low overpotential to deliver 10 and 100 mA/cm2 current density. It displays better catalytic performance with low 83.3 mV/dec Tafel slope and small charge transfer resistance of 30.6 Ω. Hence, excellent HER activity may be ascribed due to existence of high surface area, unique one-dimensional morphology and synergetic effect between strontium and vanadium oxides. [ABSTRACT FROM AUTHOR]

[Display omitted] • Unique flower- and spindle-like rods of SrMoO 4 material were explored. • Material revealed OER activity with elevated 409 F/g specific capacitance. • 1:5 M SrMoO 4 showed excellent catalytic activity toward OER. • OER showed 304 mV low overpotential and small 20.5 mV/dec Tafel slope. • SM2 electrode showed better durability during16 h chronoamperometry test. Novel and cost-effective electrocatalysts are most important materials considered for the renewable energy conversion applications. Metal molybdates have gained great attention because of oxygen evolution reaction (OER). These products still need to be improved for practical applications. In this work, SrMoO 4 nanostructures were successfully synthesized via trouble-free co-precipitation method. Scheelite-type tetragonal-phase SrMoO 4 nanostructures were substantiated using X-ray diffraction. Raman spectra confirmed existence of Mo O 4 2 - group whereas Fourier transform infrared spectra corroborated different functional groups in well-crystallized SrMoO 4 material. Morphologies of the prepared SrMoO 4 nanostructures were identified by using the scanning electron microscopy images. The high surface area and porosity of electrocatalysts significantly enhanced the electrochemical performance. Then, the surface area, pore diameter and pore volume of SM2 were 13 m2/g, 4.474 nm and 0.004 cc/g, respectively. The existence of unique flower like morphology and spindle-like rods of SrMoO 4 material confirmed the OER activity with elevated 409 F/g specific capacitance. Compared to different molar ratios of SrMoO 4 materials, 1:5 M ratios of SrMoO 4 nanostructures showed outstanding catalytic action toward OER performance with 187 mV at 10 mA/cm2 and a small 20.5 mV/dec Tafel slope. In addition, SM2 electrode showed better durability in 16 h chronoamperometry test without any decay. Therefore, optimizing the proper molar ratio of SrMoO 4 material is one of the important parameters to obtain a good candidate for electrochemical water-splitting applications. [ABSTRACT FROM AUTHOR]

[Display omitted] • CW1, CW2 and CW3 electrodes overpotential were 123, 115 and 102 mV. • Tafel slope values of prepared electrodes were 245, 244 and 238 mV/dec. • CW3 electrode exhibited high C dl value of 32.8 mF/cm2 and enhanced HER. • CW3 electrode exhibited 75% retention in 16 h durability test. Hexamethylenetetramine (HMT) assisted calcium tungstate nanostructures were successfully synthesized through co-precipitation method. The phase and material confirmation of scheelite type calcium tungstate nanostructures with tetragonal unit cell (a = 5.193 and c = 11.255) were done by employing X-ray diffraction (XRD). All the prepared electrocatalysts such as CW1, CW2 and CW3 crystallite sizes were 29.01, 24.86 and 17.40 nm respectively. The calculated band gap values were found to be 3.31, 3.31 and 3.27 eV for CW1, CW2 and CW3 materials respectively. Different morphology such as ball like and dumbbell shaped calcium tungstate were revealed by scanning electron microscopy (SEM). Surfactant largely plays a significant role to reduce nanostructures agglomeration. The specific surface area, pore volume and diameter of 0.1 M hexamethylenetetramine (HMT) assisted calcium tungstate nanostructure was about 24.7 m2/g, 0.141 cc/g and 3.365 nm. The surface area of the calcium tungstate nanostructures drastically enhanced hydrogen evolution reaction (HER) performance as recognized by linear sweep voltammetry. The overpotential values of CW1, CW2 and CW3 electrodes were 123, 115 and 102 mV respectively. Solution resistance (R s) and charge transfer resistance (R ct) of synthesized materials was finding out by electrochemical impedance spectroscopy and all prepared electrocatalyst estimated values were 1.07, 1.25, 1.34 Ω and 4.06, 1.62, 0.76 Ω respectively. The stability of 0.1 M hexamethylenetetramine (HMT) assisted CaWO 4 was analyzed by 16 h and it exhibited excellent robustness without any decay. The synthesized CaWO 4 material exhibited superior hydrogen evolution reaction (HER) activity and the prepared electrodes was capable electro catalysts in water splitting applications. [ABSTRACT FROM AUTHOR]

• Rhombohedral phase of MnCO 3 nanostructures was determined. • MnCO 3 @15 ml EG electrode exhibited a small Tafel slope value. • MnCO 3 @15 ml EG enhanced its catalytic performance. • Exhibited high current density 257 mA/g with low 184 mV overpotential. • Photocatalytic MnCO 3 hydrogen production was explored. In this research, manganese carbonate nanostructures were prepared employing simple co-precipitation route using ethylene glycol. Rhombohedral phase of MnCO 3 nanostructures was determined by X-ray diffraction. MnCO 3 @15 ml EG electrode exhibited small Tafel slope value and significantly facilitating its OER performance. The fabricated electrode materials of MnCO 3 nanostructure exhibited high 257 mA/g current density with low 184 mV overpotential. The prepared electrodes explored excellent OER performance and good stability over 16 h without degradation. Organic additive of ethylene glycol tuning its morphology to favor of OER activity and it enhanced the electrochemical performance of MnCO 3 nanomaterial. MnCO 3 material was also subjected to photocatalytic hydrogen production. There was no activity noticed in the pure water even after 3 h of experiments. The following factor may enhance the H 2 evolution rate. They are introducing hetero-atoms in crystal lattice points, combination with carbon materials such as GO, g-C 3 N 4 etc and composed of heterostructures with some other material such as TMDs, CdS, TiO 2 and ZnS etc. Hence, mono metal carbonate of MnCO 3 doesn't show any H 2 activity and the fabricated electrode was suitable candidate for oxygen evolution reaction. [ABSTRACT FROM AUTHOR]