Novel 13X Zeolite/PANI electrocatalyst for hydrogen and oxygen evolution reaction

In this work, first 13X zeolite was prepared by the hydrothermal method. Then, the composite electrode was fabricated by using 13X zeolite and aniline monomer in nickel foam by electropolymerization technique in an acidic medium (13X/PANI). The synthesized 13X zeolite was characterized by physicochemical characterization techniques such as Fourier transform infra-red (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HR-TEM), X-ray diffraction (XRD) pattern and nitrogen sorption isotherm. 13X/PANI composite was further analyzed by XRD, XPS and FE-SEM techniques. Furthermore, the catalyst activity of the synthesized 13X, PANI and 13X/PANI composite electrodes was evaluated in hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) by using linear square voltammetry (LSV) and Tafel slope method. The Tafel slopes of HER were found to be 203 mV dec⁻¹, 440 mV dec⁻¹ and 282 mV dec⁻¹ for 13X, PANI and 13X/PANI-15 electrodes respectively. While the OER Tafel slopes were found to be 423 mV dec⁻¹, 310 mV dec⁻¹ and 168 mV dec⁻¹ for 13X, PANI and 13X/PANI-15, respectively. 13X/PANI-15 electrodes show excellent catalytic performance about the overpotential at 10 mA cm⁻² for HER and the overpotential at 20 mA cm⁻² for OER. The obtained results suggest fabricated novel electrodes are a potential candidate for HER and OER reaction and can be open new avenue for other electrochemical reactions.     

Mesoporous nickel-sulfide/nickel/N-doped carbon as HER and OER bifunctional electrocatalyst for water electrolysis

The development of non-precious metal-based highly active bi-functional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is critical factor for making water electrolysis a viable process for large-scale industrial applications. In this study, bi-functional water splitting electrocatalysts in the form of nickel-sulfide/nickel nanoparticles integrated into a three-dimensional N-doped porous carbon matrix, are prepared using NaCl as a porous structure-forming template. Microstructures of the catalytic materials are characterized by scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy and N₂ adsorption-desorption analysis. The most active catalyst synthesized in this study exhibits a low HER overpotential of 70 mV at 10 mA cm⁻² and a low Tafel slope of 45 mV dec⁻¹. In OER, the optimized sample performs better than a state-of-the-art RuO₂ catalyst and produces an overpotential of 337 mV at 10 mA cm⁻², lower than that of RuO₂. The newly obtained materials are also used as HER/OER electrocatalysts in a specially assembled two-electrode water splitting cell. The cell demonstrates high activity and good stability in overall water splitting.     

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.     

Green synthesized N-doped graphitic carbon sheets coated carbon cloth as efficient metal free electrocatalyst for hydrogen evolution reaction

Heteroatom doped carbon structures received a great attention owing to its applications in catalysis, energy and optics. In this work, a simple hydrothermal approach for the synthesis of nitrogen doped graphitic carbon sheets (N-GCSs) is reported. Rubus parvifolius (R. parvifolius) fruit juice and aqueous ammonia are used as carbon precursor and nitrogen dopant, respectively. The synthesized N-GCSs are characterized using Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), Raman spectroscopy, high resolution transmission electron microscopy (HR-TEM) and field emission scanning electron microscopy (FE-SEM) coupled with energy dispersive spectrum (EDS). The presence of hydroxyl and carbonyl functionalities in the synthesized N-GCSs are confirmed by the FT-IR analysis. The doping of nitrogen in N-GCSs is revealed through the XPS spectrum. The XRD and Raman studies imply that the synthesized N-GCSs are moderate graphitic nature. The FE-SEM and HR-TEM images of N-GCSs exposed its sheet like porous morphology. The electrocatalytic activity of N-GCSs coated carbon cloth (N-GCSs/CC) are examined towards hydrogen evolution reaction (HER) in 0.50 M H₂SO₄ using linear sweep voltammetry (LSV), Tafel and electrochemical impedance spectroscopy (EIS) studies. The onset potential of synthesized N-GCSs/CC is about ?0.25 V_RHE, which is lower than that of bare carbon cloth (CC) ?0.75 V_RHE. The Tafel slope of N-GCSs/CC is smaller (198 mV dec^?1) than that of bare CC (253 mV dec^?1), suggested fast kinetics of N-GCSs. Moreover, the N-GCSs/CC is attained ?10 mA cm^?2 of current density at very low over potential of ?0.320 V_RHE. The EIS studies also proved the excellent catalytic activity of N-GCSs/CC towards HER. Thus, the R. parvifolius derived N-GCSs is a better candidate for HER in acidic medium.     

Three-dimensional Ni2P–MoP2 mesoporous nanorods array as self-standing electrocatalyst for highly efficient hydrogen evolution

Electrochemical hydrogen evolution reaction (HER) via the splitting of water has required electrocatalysts with cost-effectiveness, environmentally friendliness, high catalytic activity, and superior stability to meet the hydrogen economy in future. In this context, we report the successful synthesis of self-standing mesoporous Ni₂P–MoP₂ nanorod arrays on nickel foam (Ni₂P–MoP₂ NRs/3D-NF) through an effective phosphidization of the corresponding NiMoO₄ NRs/3D-NF. The as-synthesis Ni₂P–MoP₂ NRs/3D-NF, as an efficient HER electrocatalyst, exhibits small overpotential of 82.2 and 124.7 mV to reach current density of 10 and 50 mA cm⁻², a low Tafel slope of 52.9 mV dec⁻¹ and it retains its catalytic performance for at least 20 h in alkaline condition. Our work also offers a new strategy in designing and using transition metal phosphide-based 3D nanoarrays catalysts with enhanced catalytic efficiency for mass production of hydrogen fuels.     

Vanadium doped cobalt phosphide nanorods array as a bifunctional electrode catalyst for efficient and stable overall water splitting

For the sake of sustainable development, water splitting without other pollutants has been a candidate technology in green energy. Due to the low efficiency of water splitting, innovative breakthroughs are desirable to improve efficiency significantly. Nowadays, the rational design of non-precious metal-based robust bifunctional catalysts is considered to be a feasible way to promote both the cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER). Herein, we proposed a vanadium doped CoP nanorods array catalyst grown on carbon cloth (V–CoP NRs/CC) as a bifunctional electrode material. When V–CoP NRs/CC employed as both anode and cathode materials, it only demands low cell voltages of 1.491 V and 1.606 V to drive a current density of 10 mA cm^?2 (j₁₀) and 50 mA cm^?2 (j₅₀) in 1 M KOH alkaline electrolyte. Especially, V–CoP NRs/CC can maintain its outstanding electrocatalytic performance for more than 40 h at j₅₀ in overall water splitting.     

Synthesis of hexagonal WO3 nanocrystals with various morphologies and their enhanced electrocatalytic activities toward hydrogen evolution

The hydrogen evolution reaction (HER) achieved via electrochemical and photoelectrochemical measurements in an acid electrolyte (0.5 M H₂SO₄) was examined on hexagonal WO₃ photoanodes of different morphological structures comprised of WO₃ nanotubes (NT), nanorods (NR) and nanospheres (NS). The WO₃ synthesized using free (NR) and inorganic templates (NS and NT) thru a new sonication/hydrothermal route was comprehensively characterized utilizing XRD, TEM-SAED, photoluminescence, UV–Vis diffuse reflectance, Raman, FTIR and N₂ adsorption techniques. Herein, the WO₃ NT with an average diameter of 2.9 nm and energy gap of 2.3 eV shows the best HER activity with an overpotential of −500 mV to offer a current density of 8.0 mA cm⁻² that strikingly enhanced into 14 mA cm⁻²; at −410 mV, under visible light illumination (λ > 420). The electrochemical properties determined by cyclic voltammetry, EIS and Tafel plots argued that the activity of WO₃ NT is accelerated due to small size, enhanced wettability (WO₃.H₂O); so as to facilitating the reaction with the electrolyte, together with the 1D assisted electron transfer. It was also emphasized that the HER activity is mainly controlled by the high oxygen vacancies; emphasized via XPS technique, decreased resistances and crystal orientations when using WO₃ NTs rather than the high surface texturing properties devoted for the WO₃ NRs (S_BET = 54.3 m² g⁻¹, V_p = 0.084 cm³ g⁻¹, pore radius = 6.5 nm). This wok provides a new approach for synthesizing a free Pt WO₃ NTs photo-electrocatalyst with excellent stability; towards a remarkable HER, as examined via chronopotentiometry technique for 100 h.     

Sn self-doped α-Fe2O3 nanobranch arrays supported on a transparent,conductive SnO2 trunk to improve photoelectrochemical water oxidation

We produced hierarchically branched Fe₂O₃ nanorods on a Sb:SnO₂ transparent conducting oxide (TCO) nanobelt structure as photoanodes for photoelectrochemical water splitting. Single-crystalline SnO₂ nanobelts (NBs) surrounded by Fe₂O₃ nanorods (NRs) were synthesized by thermal evaporation, then underwent chemical bath deposition and annealing. When Fe₂O₃ was crystallized by annealing, Sn was diffused from SnO₂ NBs and incorporated to Fe₂O₃ NRs, which was confirmed through Energy dispersive spectroscopy. Unlike previous high temperature sintering (∼800 °C), Sn doped hematite NRs were obtained at a low temperature (∼650 °C). This occurred since SnO₂ NBs directly connected to Fe₂O₃ NRs are an abundant source of Sn dopant. The 3D hematite NRs on SnO₂ NBs annealed at 650 °C produce a photocurrent density of 0.88 mA/cm² at 1.23 V vs. RHE, which is 3 times higher than that of hematite NRs on a fluorine doped tin oxide (FTO) glass substrate annealed at the same temperature. The enhanced photocurrent is attributed to the improved electrical conductivity of Fe₂O₃ NRs by Sn doping, the efficient electron transport pathway by TCO nanowire and the increased surface area by hierarchically branched structure.     

MoS2/NiFeS2 heterostructure as a highly efficient electrocatalyst for overall water splitting at high current densities

Searching for efficient, stable and low-cost nonprecious catalysts for oxygen and hydrogen evolution reactions (OER and HER) is highly desired in overall water splitting (OWS). Herein, presented is a nickel foam (NF)-supported MoS₂/NiFeS₂ heterostructure, as an efficient electrocatalyst for OER, HER and OWS. The MoS₂/NiFeS₂/NF catalyst achieves a 500 mA cm⁻² current density at a small overpotential of 303 mV for OER, and 228 mV for HER. Assembled as an electrolyzer for OWS, such a MoS₂/NiFeS₂/NF heterostructure catalyst shows a quite low cell voltage (≈1.79 V) at 500 mA cm⁻², which is among the best values of current non-noble metal electrocatalysts. Even at the extremely large current density of 1000 mA cm⁻², the MoS₂/NiFeS₂/NF catalyst presents low overpotentials of 314 and 253 mV for OER and HER, respectively. Furthermore, MoS₂/NiFeS₂/NF shows a ceaseless durability over 25 h with almost no change in the cell voltage. The superior catalytic activity and stability at large current densities (>500 mA cm⁻²) far exceed the benchmark RuO₂ and Pt/C catalysts. This work sheds a new light on the development of highly active and stable nonprecious electrocatalysts for industrial water electrolysis.     

Facile process to utilize carbonaceous waste as a carbon source for the synthesis of low cost electrocatalyst for hydrogen production

Low cost non-noble metal electrocatalysts are highly desirable for the sustainable production of hydrogen as a renewable energy source. Molybdenum carbide (Mo₂C) has been considered as the promising non-noble metal electrocatalyst for the hydrogen production via hydrogen evolution reaction (HER) through water splitting. The nanostructured nitrogen (N) incorporated carbon (C) coupled with Mo₂C is the potential candidate to boost the HER activity and electrode material for the energy conversion applications. In this work, nitrogen incorporated carbon coated Mo₂C (Mo₂C@C/N) has been synthesized in an eco-friendly way using waste plastic as the carbon source. The pure phase Mo₂C@C/N has been synthesized at 700 and 800 °C for 10 h. The relatively higher temperature synthesized phase shows enhanced HER activity with lower Tafel slope (72.9 mVdec⁻¹) and overpotential of 186.6 mV to drive current density of 10 mAcm⁻². It also exhibits stability up to 2000 cyclic voltammetry (CV) cycles and retains the current density with negligible loss for 10 h. The higher temperature synthesized phase exhibits higher electrochemical active surface area (ECSA) and enhanced HER kinetics.     

Nickel foam-supported Fe,Ni-Polyporphyrin microparticles: Efficient bifunctional catalysts for overall water splitting in alkaline media

Developing highly active, stable and sustainable electrocatalysts for overall water splitting is of great importance to generate renewable H₂ for fuel cells. Herein, we report the synthesis of electrocatalytically active, nickel foam-supported, spherical core-shell Fe-poly(tetraphenylporphyrin)/Ni-poly(tetraphenylporphyrin) microparticles (FeTPP@NiTPP/NF). We also show that FeTPP@NiTPP/NF exhibits efficient bifunctional electrocatalytic properties toward both the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Electrochemical tests in KOH solution (1 M) reveal that FeTPP@NiTPP/NF electrocatalyzes the OER with 100 mA cm⁻² at an overpotential of 302 mV and the HER with 10 mA cm⁻² at an overpotential of 170 mV. Notably also, its catalytic performance for OER is better than that of RuO₂, the benchmark OER catalyst. Although its catalytic activity for HER is slightly lower than that of Pt/C (the benchmark HER electrocatalyst), it shows greater stability than the latter during the reaction. The material also exhibits electrocatalytic activity for overall water splitting reaction at a current density of 10 mA cm⁻² with a cell voltage of 1.58 V, along with a good recovery property. Additionally, the work demonstrates a new synthetic strategy to an efficient, noble metal-free-coordinated covalent organic framework (COF)-based, bifunctional electrocatalyst for water splitting.     

Performance of amine-modified CdS-D@ZIF-8 nanocomposites for enhanced photocatalytic H2 evolution

The exploration of an efficient photocatalyst for H₂ evolution directly from water splitting is highly desirable due to the current environmental and energy situation. The present work successfully used a solvothermal method to synthesize organic-inorganic CdS-diethylenetriamine (CdS-D) nanorods (NRs). The amine-modified CdS-D@ZIF-8 nanocomposite materials were prepared using the self-assembly method with different ZIF-8 nanocrystals (NCs) weight ratios. At λ ≥ 420 nm wavelength, the optimized CdS-D@ZIF-8 (CZ-2) nanocomposite with 5.0 wt% loading of ZIF-8 NCs showed the highest performance of 2293.9 μmol g⁻¹ h⁻¹ H₂ evolution and an apparent quantum yield (AQY) of 4.95%. The CZ-2 nanocomposite's activity was 114.69, 5.25, and 1.32 times higher than that of ZIF-8 NCs (20.0 μmol g⁻¹ h⁻¹), CdS-D NRs (436.4 μmol g⁻¹ h⁻¹) and 1.0 wt% Pt/CdS-D (1737.3 μmol g⁻¹ h⁻¹), respectively. The cyclic photostability of the prepared CZ-2 nanocomposite remained unchanged after six consecutive cycles. The UV-DRS, electrochemical measurements, and Mott-Schottky (MS) analysis were performed to explain the band edge positions for CdS-D NRs and ZIF-8 NCs. The detailed S-scheme charge transfer mechanism of the as-prepared catalysts was also studied using the density functional theory (DFT). This work provides vital information for the controllable synthesis of ZIF-8-modified S-scheme nanocomposites for solar energy utilization.     

Copper(II) phthalocyanine/metal organic framework electrocatalyst for hydrogen evolution reaction application

Copper(II)phthalocyanine-incorporated metal organic framework (CuPc/MOF) composite material was synthesized for application as an electrocatalyst for hydrogen evolution reaction (HER). The composite exhibited excellent electroactivity compared to the unmodified MOF, as confirmed by the diffusion coefficients (D) values of 3.89 × 10⁻⁷ and 1.57 × 10⁻⁶ cm² s⁻¹ for MOF and CuPc/MOF, respectively. The D values were determined from cyclic voltammetry (CV) experiments performed in 0.1 mol L⁻¹ tetrabutylammonium perchlorate/dimethyl sulfoxide (TBAP/DMSO) electrolyte. The Tafel slope determined from the CV data of CuPc/MOF-catalysed HER for 0.450 mol L⁻¹ H₂SO₄, was 176.2 mV dec⁻¹, which was higher than that of the unmodified MOF (158.3 mV dec⁻¹). The charge transfer coefficients of MOF and CuPc/MOF were close to 0.5, signifying the occurrence of a Volmer reaction involving either the Heyrovsky or the Tafel mechanism for hydrogen generation. For both MOF and CuPc/MOF, the exchange current density (i₀) improved with increase in the concentration of the hydrogen source (i.e. 0.033–0.45 mol L⁻¹ H₂SO₄) Nonetheless, the CuPc/MOF composite had a higher i₀ value compared with the unmodified MOF. Thus CuPc/MOF has promise as an efficient electrocatalyst for HER.     

Bamboo-like N-doped carbon tubes encapsulated Co2P–Fe2P derived from zeolitic imidazolate framework as an efficient trifunctional electrocatalyst for water splitting and Zn-air batteries

The development of high-performance and stable trifunctional electrocatalysts is a pressing challenge for the practical application of water splitting and regenerative Zn-air batteries. Herein, bamboo-like N-doped carbon tubes encapsulated Co₂P–Fe₂P nanoparticles (CoFe-PN/C) was fabricated via a facile template-sacrificial approach by using CoZn-ZIF trapping Fe³⁺ (CoFeZn/C) as the precursor. The incorporation of Fe³⁺ was achieved by the one-pot synthesis approach during crystallization of ZIF, which led to the generation of the unique bamboo-like tube structure under the condition of simultaneous phosphating and carbonization. Benefiting from the large surface area, the optimized electronic structure of active sites and the unique bamboo-like nanotube, the resultant CoFe-PN/C can be used as the trifunctional electrocatalyst possessing a small overpotential at 10 mA cm⁻² for the HER (178 mV) and OER (300 mV), as well as a high half-wave potential of 0.884 V for ORR (40 mV more positive than that of commercial 20 wt% Pt/C). Moreover, the self-designed CoFe-PN/C||CoFe-PN/C alkaline electrolyzer driving 50 mA cm⁻² only need operating potential of 1.84 V and the maximum discharge power density of the CoFe-PN/C-assembled ZABs could achieve 152.0 mW cm⁻², superior to those of Pt/RuO₂ couple. This work will facilitate the development and application of trifunctional electrocatalysts based on bi-transition metallic phosphides for energy conversion and storage technology.     

NiCoP nanoparticles anchored on CdS nanorods for enhanced hydrogen production by visible light-driven formic acid dehydrogenation

Photocatalytic dehydrogenation of formic acid (FA), HCOOH→H₂+CO₂, is a promising strategy for hydrogen production. Although tremendous efforts have been made, developing efficient and robust system driven by visible light without noble metal still remains a huge challenge. Herein, we report for the first time the use of NiCoP nanoparticles anchored on CdS nanorods (NiCoP@CdS NRs) as a highly efficient and robust catalyst for photocatalytic FA dehydrogenation. NiCoP nanoparticles as cocatalyst can effectively separate the electron-hole pairs generated by CdS NRs. The H₂ production rate of the NiCoP@CdS nanorods reached ~354 μmol mg⁻¹ h⁻¹ under visible light irradiation (λ > 420 nm) and the apparent quantum yield (AQY) was ~45.5 % at 420 nm which are among the best values ever reported in photocatalytic FA dehydrogenation systems. This work provides a prospective strategy for developing noble-metal-free photocatalytic FA dehydrogenation systems and hydrogen-based energy applications.     

Ni3S2-MoSx nanorods grown on Ni foam as high-efficient electrocatalysts for overall water splitting

In order to solve the problem of large overpotential in water electrolysis for hydrogen production, transition metal sulfides are promising bifunctional electrocatalysts for hydrogen evolution reaction/oxygen evolution reaction that can significantly reduce overpotential. In this work, Ni₃S₂ and amorphous MoS_x nanorods directly grown on Ni foam (Ni₃S₂-MoS_x/NF) were prepared via one-step solvothermal process, which were used as a high-efficient electrocatalyst for overall water splitting. The Ni₃S₂-MoS_x/NF composite exhibits very low overpotentials of 65 and 312 mV to reach 10 mA cm⁻² and 50 mA cm⁻² in 1.0 M KOH for HER and OER, respectively. Besides, it exhibits a low Tafel slope (81 mV dec⁻¹ for HER, 103 mV dec⁻¹ for OER), high exchange current density (1.51 mA cm⁻² for HER, 0.26 mA cm⁻² for OER), and remarkable long-term cycle stability. This work provides new perspective for further the development of highly effective non-noble-metal materials in the energy field.     

Ceria-based quantum dots/nanorods supported metallic cobalt for efficient photocatalytic hydrogen production

The concentration of photogenerated electrons on support surface has a significant impact on the photocatalytic performance of the corresponding catalyst. Herein, the CeO₂-based homojunction support consisted of quantum dots/nanorods (QDs/NRs) was fabricated by two-step calcination with assistance of KCI and NaCl. Based on CeO₂-QDs/NRs support, the Co-based catalyst exhibited excellent catalytic performance for photocatalytic hydrogen evolution from Ammonia Borane (NH₃BH₃). The catalysts exhibited the highest activity with TOF 96.15 min⁻¹ under optimized conditions, which was significantly improved compared Co/CeO₂ NRs (68.5 min⁻¹). Detailed structure characterizations revealed that the QDs with size range from 2 to 5 nm grow on the surface of NRs, which had capacity to transfer more photogenerated electrons from the bulk to surface compared with pristine CeO₂ NRs. Meanwhile, work function was upshifted from CeO₂ NRs to CeO₂-QDs/NRs. The synergy of two factors drove more electrons transfer from CeO₂-QDs/NRs to active metal Co, accelerating the adsorption and activation of NH₃BH₃. In addition, the forming mechanization QDs by inducing the morphological evolution of CeO₂ nanoparticles was also investigated. This work not only provides efficient photocatalyst for H₂ evolution from NH₃BH₃ but also provides new insights into the design and preparation efficient QDs-based homojunction catalyst.     

Photocatalytic hydrogen evolution from water splitting using Cu doped ZnS microspheres under visible light irradiation

Cu/ZnS microspheres have been successfully synthesized using microwave irradiation method without using any template. Cu/ZnS microspheres were characterized by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), inductively coupled plasma optima optical emission spectrometer (ICP-OES), X-ray photoelectron spectroscopy (XPS), diffused reflectance spectroscopy (DRS), and electrochemical impedance spectroscopy (EIS) methods. Tuning of band gap from 3.43 to 2.36 eV was successfully achieved upon doping copper (0–10%) into ZnS. The photocatalytic activity was investigated by photosplitting of water containing an aqueous Na₂S solution under visible light irradiation. Among the prepared photocatalysts, the hydrogen evolution rate reaches the maximum of about 973.1 μmol h⁻¹ g⁻¹ for 2.0 mol% Cu²⁺ ion doped ZnS. Moreover, Cu/ZnS microspheres were found photocatalytically stable during the 48 h test runs.     

Development of RuO2/CeO2 heterostructure as an efficient OER electrocatalyst for alkaline water splitting

Here, the synthesis of RuO₂ loaded CeO₂ with varying amount of Ru loading with enhanced amount of Ce³⁺ and surface area, through synthesis of CeO₂ using cerium ammonium carbonate complex as procure followed by Ru loading by impregnation and calcination at 300 °C, is presented. Corresponding characterizations by XRD, SEM, TEM, XPS of all the samples reveal the formation of highly crystalline mesoporous CeO₂ nanoparticles with uniformly dispersed RuO₂ particles on the CeO₂ surface having approximately 45% Ce³⁺. All the samples were utilized as oxygen evolution reaction (OER) catalyst for electrocatalytic H₂ generation through water electrolysis. Electrocatalytic experiments reveal that synthesized 1 wt% RuO₂ loaded CeO₂ (1-RuO₂/CeO₂) showed superior OER activity. A quite low over-potential of 350 mV is required to attain a current density of 10 mA/cm² (ɳ₁₀), with a Tafel slope of 74 mVdec⁻¹ for OER in 1 M KOH solution. The synthesized 1-RuO₂/CeO₂ electrocatalyst also exhibited superior long term stability in basic medium and redox atmosphere.     

Construction of P,N-codoped carbon shell coated CoP nanoneedle array with enhanced OER performance for overall water splitting

Water electrolysis to generate hydrogen (H₂) and oxygen (O₂) was a sustainable alternative for clean energy in the future but remained challenging. Herein, we fabricated a nanoneedle-like CoP core coated by a P,N-codoped carbon shell (CoP@PNC@NF). The hierarchical structure, unique nanoneedle-like morphology, CoP core, and P,N-codoped carbon shell were responsible for the high electrocatalytic activity. Electrocatalytic tests demonstrated that CoP@PNC@NF displayed low overpotentials of 137.6 and 148.4 mV, as well as Tafel slopes of 59.89 and 56.40 mV dec⁻¹ for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER), respectively, at 10 mA cm⁻² in 1.0 M KOH. The bifunctional electrocatalyst CoP@PNC@NF also exhibited a low cell voltage of 1.458 V to yield 10 mA cm⁻² in the two-electrode system and could maintain the activity for 50 h. The Faradaic efficiencies of CoP@PNC@NF for both HER and OER were nearly 100%. The result outperformed the precious-metal-based electrocatalyst apparatus (RuO₂||Pt/C) and other carbon-coated transition-metal phosphides (TMPs). This work paved the way for the rational design of carbon shell-coated TMPs with low energy barriers for converting and storing electrochemical energy.