Catalysts For Electrochemical Water Splitting Research Articles

Electrodeposition of Ni-Co-Fe mixed sulfide ultrathin nanosheets on Ni nanocones: a low-cost, durable and high performance catalyst for electrochemical water splitting.

The development of a bi-functional active and stable catalyst for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is an important challenge in overall electrochemical water splitting. In this study, firstly, nickel nanocones (NNCs) were formed using electrochemical deposition, and then Ni-Co-Fe based mixed sulfide ultrathin nanosheets were obtained by directly depositing on the surface of the nanocones using the CV method. With a hierarchical structure of Ni-Fe-Co-S nanosheets, not only was a high active surface area created, but also the electron transfer and mass transfer were enhanced. This structure also led to the faster release of hydrogen bubbles from the surface. An overpotential value of 106 mV was required on the surface of this electrode to generate a current density of 10 mA cm-2 in the HER, whereas, for the OER, 207 mV overpotential was needed to generate a current density of 10 mA cm-2. Furthermore, this electrode required 1.54 V potential to generate a current density of 10 mA cm-2 in the total electrochemical water splitting. The resulting electrode also exhibited reasonable electrocatalytic stability, and after 10 hours of electrolysis in the overall water splitting reaction, the voltage change was negligible. This study introduces a simple, efficient, reasonable and cost-effective method of creating an effective catalyst for the overall water splitting process.

High-performance Fe[sbnd]Co[sbnd]P alloy catalysts by electroless deposition for overall water splitting

At present, it is difficult for electrocatalytic electrode materials with high-Performance to be prepared at low cost and large area under mild conditions. Therefore, we adopt a facile electroless plating method to deposit the FeCoP alloys on the nickel foam (NF) with different areas of 1 cm2, 4 cm2, 8 cm2 and 16 cm2. The FeCoP/NF catalysts exhibit extraordinary catalytic activity for the oxygen evolution reaction (OER) in alkaline media and are comparable to the state-of-the-art IrO2 in 1.0 M KOH, capable of yielding a current density of 10 mA cm−2 at an overpotential of only 250 mV. Furthermore, the FeCoP/NF catalysts show efficient activity towards the hydrogen evolution reaction (HER) with an overpotential of 163 mV at j = 10 mA cm−2 as well. Remarkably, when used as both the anode and cathode, a low potential of 1.68 V (vs. RHE) is required to reach the current density of j = 10 mA cm−2, making the FeCoP/NF alloys as an active bifunctional electrocatalyst for overall water splitting. The FeCoP/NF alloy catalysts with high catalytic activity, facile preparation and low cost would provide a new pathway for the design and large-scale application of high-performance bifunctional catalysts for electrochemical water splitting.

Multimetal Borides Nanochains as Efficient Electrocatalysts for Overall Water Splitting.

The development of cost-efficient, active, and stable electrode materials as bifunctional catalysts for electrochemical water splitting is crucial to high-performance renewable energy storage and conversion devices. In this work, the synthesis of Co-based multi-metal borides nanochains with amorphous structure is reported for boosting the oxygen evolution (OER) and hydrogen evolution reactions (HER) by one-pot NaBH4 reduction of Co2+ , Ni2+ , and Fe2+ under ambient temperature. In all the investigated Co-based metal borides, NiCoFeB nanochains show the excellent OER performance with a low overpotential of 284 mV at 10 mA cm-2 and Tafel slope of 46 mV dec-1 , respectively, together with excellent catalytic stability, and robust HER performance with an overpotential of 345 mV at 10 mA cm-2 . The density functional theory (DFT) calculations reveal that the excellent electrocatalytic performance is mainly attributed to optimal electronic structure by tuning the Co-3d band activities by the incorporation of Ni and Fe for enhanced water splitting via the potentially existed Co0 state. Moreover, the electrolyzer using NiCoFeB nanochains as anode and cathode offers 10 mA cm-2 at a cell voltage of 1.81 V, comparable to commercial Pt/C // Ir/C, providing a simple method to design and explore highly efficient and cheap bifunctional electrocatalysts for overall water splitting.

Facile Synthesis of Mesoporous Nickel Cobalt Oxide for OER – Insight into Intrinsic Electrocatalytic Activity

AbstractThe development of novel metal oxide catalysts for electrochemical water splitting has been one of the future challenges in catalysis. We present the development of structured spinel based NiCo2O4 materials using in‐situ hydrothermal synthesis and KIT‐6 as a template. Their electron transfer kinetics in the oxygen evolution reaction (OER) at pH 14 are studied. Structuring of NiCo2O4 via KIT‐6 improves the intrinsic catalyst performance, e. g., a lower overpotential of ∼350 mV and a good long‐term stability could be observed compared to 385 mV and poor stability of commercially available NiCo2O4. Kinetic studies provided insights into structure‐activity relations and the nature of the electrode/electrolyte interface. Interestingly, structuring via KIT‐6 increases not only the electrochemical surface area but also the current density accompanied by superior charge transfer capacity.

Size and Electronic Modulation of Iridium Nanoparticles on Nitrogen-Functionalized Carbon toward Advanced Electrocatalysts for Alkaline Water Splitting.

Developing efficient catalytic materials for electrochemical water splitting is important. Herein, uniformly dispersed and size-controllable iridium (Ir) nanoparticles (NPs) were prepared using a nitrogen-functionalized carbon as the support (Ir/CN). We found that nitrogen functionalization can simultaneously modulate the size of Ir NPs to substantially enhance the catalytically active sites and adjust the electronic structure of Ir, thereby promoting electrocatalytic activity for water splitting. Consequently, the as-synthesized Ir/CN shows excellent electrocatalytic performance with overpotentials of 12 and 265 mV for hydrogen and oxygen evolution reactions in basic medium, respectively. These findings may pave the way for designing and synthesizing other similar materials as efficient catalysts for electrochemical water splitting.

Multifunctional (Fe0.5Ni0.5)S2 nanocrystal catalysts with high catalytic activities for reduction of I3− and electrochemical water splitting

It is important to synthesize environmentally friendly transition metal sulfide catalysts with superior performance for electrochemical water splitting and reduction of I3− in dye-sensitized solar cells (DSSCs). In this work, cubic (Fe0.5Ni0.5)S2 nanocrysals with a monodispersed size of ca. 10 nm were successfully prepared via a hot-injection reaction with a Schlenk line system. Because of the FeNi-oleate complex as transition metal source, no other by-products were produced. The (Fe0.5Ni0.5)S2 nanocrystal/carbon black composite with different nanocrystal contents was control fabricated. Because the composite possessed two merits, more catalytically active sites of nanocrystals and fast electron transfer of carbon black, it is a promising catalyst for electrochemical water splitting and reduction of I3− in DSSCs. As the counter electrode catalysts for reduction of I3−, DSSCs based on the composite with 57% (Fe0.5Ni0.5)S2 nanocrystal contents have a high power conversion efficiency of 6.71%, which was comparable to Pt-based DSSCs (7.05%). The electrochemical measurement showed that (Fe0.5Ni0.5)S2 nanocrystals had a good catalytic activity for reduction of I3−. As the catalytic electrode for hydrogen evolution reaction (HER), the composite electrode with 57% (Fe0.5Ni0.5)S2 nanocrystal contents displayed an overpotential of 250 mV to reach the current density of 10 mA cm−2 in alkaline solution. It retained good HER activity for 1000-cycle measurements. The density functional theory showed the free energy of hydrogen adsorbed on the Ni site near S defects was − 0.12 eV, which was smaller than that of the Fe site near S defects. So, the Ni site near S defects of (Fe0.5Ni0.5)S2 was the main catalytically active site for HER. Also, the (Fe0.5Ni0.5)S2 nanocrystals displayed good electrocatalytic activity for oxygen evolution reaction. This type of double metal sulfide with monodispersed size paves the way for new insight into earth-abundance catalysts for water splitting and I3− reduction.

Trends in adsorption of electrocatalytic water splitting intermediates on cubic ABO3 oxides.

The reactivity of solid oxide surfaces towards adsorption of oxygen and hydrogen is a key metric for the design of new catalysts for electrochemical water splitting. In this paper, we report on trends in the adsorption energy of different adsorbed intermediates derived from the oxidation and reduction of water for ternary ABO3 oxides in the cubic perovskite structure. Our findings support a previously reported trend that rationalizes the observed lower bound in oxygen evolution (OER) overpotentials from correlations in OH* and OOH* adsorption energies. In addition, we report hydrogen adsorption energies that may be used to estimate hydrogen evolution (HER) overpotentials along with potential metrics for electrochemical metastability in reducing environments. We also report and discuss trends between atom-projected density of states and adsorption energies, which may enable a design criteria from the local electronic structure of the active site.

3D nickel-cobalt diselenide nanonetwork for highly efficient oxygen evolution

Active, stable and low-cost oxygen evolution reaction (OER) catalyst for electrochemical water splitting is key to efficient energy conversion and storage. Here, we report a three-dimensional (3D) nanonetwork as noble-metal-free electrode consisting of nickel cobalt diselenide (NiCoSe2) nanobrush arrays on Ni foam (NF) through the initial hydrothermal reaction and subsequent thermal selenization process. Introducing ammonium fluoride as surface controller, different NiCoSe2 hierarchical architecture can be modulated from nanorods, nanobrush to nanosheets. The unique brush-like NiCoSe2 possesses high surface area for mass transfer, rough surface with rich active sites, 3D nanostructure preventing the accumulation of O2 bubbles. Compared to NiCoSe2 nanorods/NF, NiCoSe2 nanosheets/NF and commercial RuO2, NiCoSe2 nanobrush/NF exhibits an enhanced OER performance in alkaline media to reach a low overpotential of 274mV at the current density of 10mA/cm2, small Tafel slope and a long-term stability. The developed 3D nanonetwork highlights the nanoscale engineering and offers a promising alternative to noble metal catalysts for electrochemical water oxidation.

Partial-sacrificial-template Synthesis of Fe/Ni Phosphides on Ni Foam: a Strongly Stabilized and Efficient Catalyst for Electrochemical Water Splitting

Electrochemical water splitting is considered to be one of the most promising strategies for clean and efficient hydrogen production. In this paper, an in-situ growth of iron-nickel phosphide on nickel foam (FeNiPx/NF) is demonstrated as a self-supported ternary catalyst for electrochemical water splitting. The FeNiPx/NF were prepared by a thermo-reaction between NaH2PO2 and NiFe hydroxide precursors that are in situ grown on Ni foam via a simple chemical precipitation reaction. In this newly proposed method, the nickel foam not only acts as an electrode substrate, but also serves as a slow-release Ni source in the reaction due to its oxidation by Fe3+ in solution. Benefiting from collaborative advantages of bimetallic composite, metallic phosphide, and unique electrode fabrication, the FeNiPx/NF exhibits extraordinarily high activities for both OER and HER with low overpotentials of of 192 and 106mV at 10mAcm−2, 236 and 161mV at 100mAcm−2, respectively. The voltage during the galvanostatic electrolysis is well maintained for almost 400h without any visible elevation, representing the few most stable noble-metal-free catalysts for water splitting.

Recent advances in metal–nitrogen–carbon catalysts for electrochemical water splitting

The recent developments of metal–nitrogen–carbon catalysts for electrochemical water splitting have been comprehensively summarized.

Simultaneous co-doping of RuO2 and IrO2 into anodic TiO2 nanotubes: A binary catalyst for electrochemical water splitting

The simultaneous doping of RuO2 and IrO2 catalysts into anodic TiO2 nanotubes (NTs) was successfully achieved by single-step anodization. KRuO4 was used as the precursor for the RuO2 dopant. However, for IrO2 doping, IrOx nanoparticles (NPs) were synthesized from IrCl3 as an intermediate species to avoid damage to the NTs by chloride ions during doping. IrO4− generated from the IrOx NPs through selective dissolution in the electrolyte was simultaneously doped into the positively biased TiO2 NTs along with RuO2. The structural features, NT length, and amount of catalyst doping were controlled by the concentration of HF in the electrolyte and the anodizing time. The binary-catalyst-doped TiO2 NTs exhibited an outstanding onset potential of 0.84 V for the oxygen evolution reaction (OER). In addition, the amount of O2 gas evolved during the OER at 2.0 V was measured to be 230 μmol cm−2 min−1 by gas chromatography, which corresponds to a faradaic efficiency of 99%. The major oxidation states of the metals in the catalysts were found to be Ru4+ and Ir4+ by X-ray photoelectron spectroscopy and transmission electron microscopy selected area electron diffraction analysis, indicating the presence of RuO2 and IrO2 in the TiO2 NTs.

The urchin-like sphere arrays Co3O4 as a bifunctional catalyst for hydrogen evolution reaction and oxygen evolution reaction

Abstract Electrochemical water splitting has attracted great interest because of the growing demand for sustainable energy and increasing concerns for the environment. We present a facile strategy to design the three-dimensional (3D) urchin-like sphere arrays Co3O4 as an effective bifunctional catalyst for electrochemical water splitting. The 3D urchin-like Co3O4 was directly grown on Ni foam by a hydrothermal reaction and annealing treatment at a low temperature. This process offers several advantages including facile synthesis, binder-free, and low cost. The 3D urchin-like Co3O4 as a catalyst for hydrogen evolution reaction exhibits a low onset potential (−130 mV vs. RHE) and good cycling stability in an alkaline electrolyte. When urchin-like Co3O4 is used as a catalyst for oxygen evolution reaction, the onset potential is at 1.46 V (vs. RHE) with a low overpotential of only 230 mV. The good catalytic activity can be attributed to the unique urchin-like nanostructure, abundant mesopores, and low charge-transfer resistance (compared with Co3O4 NPs). In addition, H2 and O2 generation was performed using Co3O4 as both cathode and anode catalysts with a potential of 1.64 V to reach a current density of 10 mA cm−2.

Low Overpotential Water Splitting Using Cobalt–Cobalt Phosphide Nanoparticles Supported on Nickel Foam

We report a simple, facile, and safe route for preparation of cobalt–cobalt phosphide (Co/Co2P) nanoparticles and demonstrate their application as efficient low-cost catalysts for electrochemical water splitting. The catalyst achieves good performance in catalyzing both the cathode and anode half-cell water-splitting reactions in 1.0 M KOH and the hydrogen evolution reaction in an acidic electrolyte, 0.5 M H2SO4. For the oxygen evolution reaction in 1.0 M KOH, a current of 10 mA cm–2 was attained at 0.39 V overpotential on a glassy carbon electrode, while an overpotential of 0.19 V was attained at 50 mA cm–2 when the catalyst was supported on nickel foam.

Nanostructured catalysts for electrochemical water splitting: current state and prospects

The fundamentals of water electrolysis, current popular electrocatalysts developed for cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) in liquid electrolyte water electrolysis are reviewed and discussed.

The goldilocks electrolyte: examining the performance of iron/nickel oxide thin films as catalysts for electrochemical water splitting in various aqueous NaOH solutions

A rigorous study of electrodeposited Ni/Fe oxides for the OER was performed in three different sodium hydroxide electrolytes with various Fe impurity concentrations.

Co-Doped MoS₂ Nanosheets with the Dominant CoMoS Phase Coated on Carbon as an Excellent Electrocatalyst for Hydrogen Evolution.

Highly active and low-cost catalysts for hydrogen evolution reaction (HER) are crucial for the development of efficient water splitting. Molybdenum disulfide (MoS2) nanosheets possess unique physical and chemical properties, which make them promising candidates for HER. Herein, we reported a facile, effective, and scalable strategy by a deposition-precipitation method to fabricate metal-doped (Fe, Co, Ni) molybdenum sulfide with a few layers on carbon black as noble metal-free electrocatalysts for HER. The CoMoS phase after thermal annealing in Co-doped MoS2 plays a crucial role for the enhanced HER. The optimized Co-doped MoS2 catalyst shows superior HER performance with a high exchange current density of 0.03 mA·cm(-2), low onset potential of 90 mV, and small Tafel slope of 50 mV·dec(-1), which also exhibits excellent stability of 10000 cycles with negligible loss of the cathodic current. The superior HER activity originates from the synergistically structural and electronic modulations between MoS2 and Co ions, abundant defects in the active edge sites, as well as the good balance between active sites and electronic conductivity. Thanks to their ease of synthesis, low cost, and high activity, the Co-doped MoS2 catalysts appear to be promising HER catalysts for electrochemical water splitting.

Oxide‐Supported IrNiOx Core–Shell Particles as Efficient, Cost‐Effective, and Stable Catalysts for Electrochemical Water Splitting

AbstractActive and highly stable oxide‐supported IrNiOx core–shell catalysts for electrochemical water splitting are presented. IrNix@IrOx nanoparticles supported on high‐surface‐area mesoporous antimony‐doped tin oxide (IrNiOx /Meso‐ATO) were synthesized from bimetallic IrNix precursor alloys (PA‐IrNix /Meso‐ATO) using electrochemical Ni leaching and concomitant Ir oxidation. Special emphasis was placed on Ni/NiO surface segregation under thermal treatment of the PA‐IrNix /Meso‐ATO as well as on the surface chemical state of the particle/oxide support interface. Combining a wide array of characterization methods, we uncovered the detrimental effect of segregated NiO phases on the water splitting activity of core–shell particles. The core–shell IrNiOx /Meso‐ATO catalyst displayed high water‐splitting activity and unprecedented stability in acidic electrolyte providing substantial progress in the development of PEM electrolyzer anode catalysts with drastically reduced Ir loading and significantly enhanced durability.

Oxide-supported IrNiO(x) core-shell particles as efficient, cost-effective, and stable catalysts for electrochemical water splitting.

Active and highly stable oxide-supported IrNiO(x) core-shell catalysts for electrochemical water splitting are presented. IrNi(x)@IrO(x) nanoparticles supported on high-surface-area mesoporous antimony-doped tin oxide (IrNiO(x)/Meso-ATO) were synthesized from bimetallic IrNi(x) precursor alloys (PA-IrNi(x) /Meso-ATO) using electrochemical Ni leaching and concomitant Ir oxidation. Special emphasis was placed on Ni/NiO surface segregation under thermal treatment of the PA-IrNi(x)/Meso-ATO as well as on the surface chemical state of the particle/oxide support interface. Combining a wide array of characterization methods, we uncovered the detrimental effect of segregated NiO phases on the water splitting activity of core-shell particles. The core-shell IrNiO(x)/Meso-ATO catalyst displayed high water-splitting activity and unprecedented stability in acidic electrolyte providing substantial progress in the development of PEM electrolyzer anode catalysts with drastically reduced Ir loading and significantly enhanced durability.

A sea anemone-like CuO/Co3O4 composite: an effective catalyst for electrochemical water splitting.

A facile unipolar pulse electrodeposition combined with the thermal oxidation method was applied for fabrication of CuO/Co3O4 composites on carbon electrode for water electrolysis, and it was found that the sea anemone-like one with a 3D hierarchical structure formed at -0.8 V exhibited excellent performance for water electrolysis at a low overpotential with high stability.

MoS2-based materials as alternative cathode catalyst for PEM electrolysis

Pt and Ir are the most popular catalysts for electrochemical water splitting, but their low abundance on Earth's crust and high price render them unsustainable for future use. In the quest for alternative catalyst materials, a popular hydro-treating catalyst, molybdenum disulphide (MoS2), has been found to be promising for hydrogen evolution reaction (HER). Two types of MoS2-carbon composites, (i) physical mixture of MoS2 and carbon black (Vulcan®) and (ii) MoS2 supported on reduced graphene oxide (RGO), were examined. Among the MoS2-based materials tested, 47 wt% MoS2/Vulcan® gave the best performance in terms of current density at an encouraging level for practical application. The poor performance of bare MoS2 was attributed to its poor electrical conductivity. No indication of performance deterioration was observed for 18 h of continuous operation at 2.0 V cell voltage with 47 wt% MoS2/Vulcan®. MoS2/RGO hybrids showed HER activity, which was considerably higher than that of bare MoS2.