Efficiency For Overall Water Splitting Research Articles

Interfacial electronic modulation of NiCo decorated nano-flowered MoS2 on carbonized wood as a remarkable bifunctional electrocatalyst for boosting overall water splitting

The development of a cost-effective and efficient bifunctional electrode for overall water splitting holds significant importance in accelerating the sustainable advancement of hydrogen energy. The present study involved a bifunctional catalytic electrode was prepared by loading NiCo-modified 1T/2H MoS2 onto carbonized wood (NiCo-MoS2-CW) using the hydrothermal and electrodeposition techniques. The XPS analysis revealed that NiCo-modified MoS2 exhibited a weak electron characteristic, which facilitated the ionization of H2O and significantly enhanced the Volmer step. The XPS analysis unveiled that NiCo-modified MoS2 displayed a weak electron characteristic, thereby promoting the ionization of H2O and substantially augmenting the Volmer step. The electrocatalytic performance of the NiCo-MoS2-CW in 1.0 M KOH is remarkably impressive, exhibiting minimal overpotentials of only 64 mV (10 mA cm−2) and 216 mV (50 mA cm−2) for the hydrogen evolution reaction and oxygen evolution reaction, respectively. The NiCo-MoS2-CW || NiCo-MoS2-CW electrolytic cell can achieve a cell voltage of only 1.69 V to achieve a current density of 50 mA cm−2. Overall, this study proposes a potential approach to improve the catalytic efficiency of overall water splitting by modulating the interfacial electronic properties of MoS2.

Regulating Mo-based alloy-oxide active interfaces for efficient alkaline hydrogen evolution assisted by hydrazine oxidation

Improving the efficiency of overall water splitting (OWS) is crucial due to the slow four-electron transfer process in the oxygen evolution reaction (OER). The coupling of the thermodynamically favorable hydrazine oxidation reaction (HzOR) with the hydrogen evolution reaction (HER) significantly boosts hydrogen production. A Ru-decorated MoNi/MoO2 micropillar (Ru-MoNi/MoO2) has been synthesized using a hydrothermal followed by reduction annealing. Benefiting from Ru moderating the active interface of Mo-based alloys/oxides and the unique one-dimensional micropillar morphology. The synthesized Ru-MoNi/MoO2 exhibits outstanding bifunctional activity for HER and HzOR, achieving 10 mA cm−2 at merely −13 mV and −34 mV in 1 M KOH and 1 M KOH + 0.5 M N2H4, respectively. Notably, with Ru-MoNi/MoO2 in a dual-electrode setup, only 0.57 V is needed to achieve 50 mA cm−2, demonstrating good stability and facilitating hydrazine-assisted water splitting (OHzS). This work offers insights into the modulation of alloy/metal oxide active interfaces, contributing to the development of efficient bifunctional catalysts for HER and HzOR.

Superaerophilic/Superaerophobic NiFe-LDHs Electrode for Enhancing Overall Water Splitting in Alkaline Media.

Overall water splitting, as a critical approach to producing green hydrogen, is greatly impeded by the mass transfer of gaseous bubbles and dissolved gas molecules. Herein, a bifunctional superaerophilic/superaerophobic (SAL/SAB) NiFe layered-double-hydroxides (LDHs) electrode has been developed, which can drive H2 and O2 bubbles out of the reaction system by asymmetric Laplace pressure and accelerate dissolved gases diffusion through reducing their diffusion distance. Consequently, the SAL/SAB NiFe-LDHs electrode exhibits excellent HER activity with an overpotential of -76 mV at -10 mA cm-2 and outstanding oxygen evolution reaction activity with an overpotential of 253 mV at 100 mA cm-2. The bifunctional SAL/SAB NiFe-LDHs electrode is further utilized in overall water splitting, which can achieve 10 mA cm-2 with a cell voltage of 1.54 V. This work provides an efficient strategy to improve the efficiency of overall water splitting and can stimulate new electrode design in various gas-involved processes.

Cobalt-Doping Induced Formation of Five-Coordinated Nickel Selenide for Enhanced Ethanol Assisted Overall Water Splitting.

To overcome the low efficiency of overall water splitting, highly effective and stable catalysts are in urgent need, especially for the anode oxygen evolution reaction (OER). In this case, nickel selenides appear as good candidates to catalyze OER and other substitutable anodic reactions due to their high electronic conductivity and easily tunable electronic structure to meet the optimized adsorption ability. Herein, an interesting phase transition from the hexagonal phase of NiSe (H-NiSe) to the rhombohedral phase of NiSe (R-NiSe) induced by the doping of cobalt atoms is reported. The five-coordinated R-NiSe is found to grow adjacent to the six-coordinated H-NiSe, resulting in the formation of the H-NiSe/R-NiSe heterostructure. Further characterizations and calculations prove the reduced splitting energy for R-NiSe and thus the less occupancy in the t2g orbits, which can facilitate the electron transfer process. As a result, the Co2 -NiSe/NF shows a satisfying catalytic performance toward OER, hydrogen evolution reaction, and (hybrid) overall water splitting. This work proves that trace amounts of Co doping can induce the phase transition from H-NiSe to R-NiSe. The formation of less-coordinated species can reduce the t2g occupancy and thus enhance the catalytic performance, which might guide rational material design.

CdS@Au micro-spheres as an active and durable bifunctional catalyst for the urea-assisted H2 evolution reaction

Hydrogen evolution reaction (HER) and urea oxidation reaction (UOR) limit the efficiency of overall water splitting and urea oxidation for hydrogen generation, respectively. In this paper, we synthesize CdS@Au catalysts with excellent electrocatalytic activity for HER and UOR by a simple condensate reflux method. Using urea oxidation as an alternative anode reaction, the anodic oxidation potential decreased significantly to 286.4 mV@10 mA cm−2. With CdS@Au as the anode, the cell voltage drops to 1.34 V@10 mA cm−2. By discussing the Au content, it was shown that Au has a strong Lewis acidity and electronegativity, favoring hydrogen evolution.

Prussian Blue Analogue-Assisted Formation of Iron–Nickel Selenide Porous Nanosheets for Enhanced Oxygen Evolution

The development of active and stable electrocatalysts made from earth-abundant elements to accelerate the oxygen evolution reaction (OER) kinetics is of great significance for improving the efficiency of overall water splitting. Herein, a Prussian blue analogue (PBA)-assisted strategy to synthesize FeSe–NiSe nanosheets is reported. With this approach, porous FeSe–NiSe nanosheets supported on conductive Ni foam (NF) are fabricated via controlled chemical etching of Ni(OH)2/NF with Fe(CN)63– and subsequent selenylation treatment. The as-derived FeSe–NiSe/NF electrode with unique interpenetrated porous three-dimensional (3D) network architecture successfully combines the desired merits including high conductivity and a large specific surface area. As a result, it exhibits enhanced electrocatalytic OER performance in alkaline media, which requires overpotentials of only 234 and 268 mV to deliver current densities of 10 and 100 mA cm–2, respectively, outclassing its counterpart NiSe/NF. Furthermore, the catalyst possesses a very low Tafel slope (22 mV dec–1) and excellent durability.

2D Metal-Organic Frameworks as Competent Electrocatalysts for Water Splitting.

Hydrogen, a clean and flexible energy carrier, can be efficiently produced by electrocatalytic water splitting. To accelerate the sluggish hydrogen evolution reaction and oxygen evolution reaction kinetics in the splitting process, highly active electrocatalysts are essential for lowering the energy barriers, thereby improving the efficiency of overall water splitting. Combining the distinctive advantages of metal-organic frameworks (MOFs) with the physicochemical properties of 2D materials such as large surface area, tunable structure, accessible active sites, and enhanced conductivity, 2D MOFs have attracted intensive attention in the field of electrocatalysis. Different strategies, such as improving the conductivities of MOFs, reducing the thicknesses of MOF nanosheets, and integrating MOFs with conductive particles or substrates, are developed to promote the catalytic performances of pristine MOFs. This review summarizes the recent advances of pristine 2D MOF-based electrocatalysts for water electrolysis. In particular, their intrinsic electrocatalytic properties are detailly analyzed to reveal important roles of inherent MOF active centers, or other in situ generated active phases from MOFs responsible for the catalytic reactions. Finally, the challenges and development prospects of pristine 2D MOFs for the future applications in overall water splitting are discussed.

Oxygen Evolution Electrocatalysts for the Proton Exchange Membrane Electrolyzer: Challenges on Stability.

Hydrogen generated by proton exchange membrane (PEM) electrolyzer holds a promising potential to complement the traditional energy structure and achieve the global target of carbon neutrality for its efficient, clean, and sustainable nature. The acidic oxygen evolution reaction (OER), owing to its sluggish kinetic process, remains a bottleneck that dominates the efficiency of overall water splitting. Over the past few decades, tremendous efforts have been devoted to exploring OER activity, whereas most show unsatisfying stability to meet the demand for industrial application of PEM electrolyzer. In this review, systematic considerations of the origin and strategies based on OER stability challenges are focused on. Intrinsic deactivation of the material and the extrinsic balance of plant-induced destabilization are summarized. Accordingly, rational strategies for catalyst design including doping and leaching, support effect, coordination effect, strain engineering, phase and facet engineering are discussed for their contribution to the promoted OER stability. Moreover, advanced in situ/operando characterization techniques are put forward to shed light on the OER pathways as well as the structural evolution of the OER catalyst, giving insight into the deactivation mechanisms. Finally, outlooks toward future efforts on the development of long-term and practical electrocatalysts for the PEM electrolyzer are provided.

Carbon nitride photocatalyst with internal electric field induced photogenerated carriers spatial enrichment for enhanced photocatalytic water splitting

Photocatalytic water splitting is a cost-effective way to convert sustainable solar energy into chemical energy. Among various photocatalytic systems, coupling the H2- and O2- evolving photocatalysts has been widely used in photocatalytic water splitting. However, due to the close spatial distance between surface electrons and surface holes, this heterogeneous material easily catalyzes the unwanted reverse reaction, limiting the solar energy conversion efficiency. Here we present a carbon nitride nanosheet (CNN) homojunction which possesses electrons-enriched region and holes-enriched region induced by the interfacial internal electric field. The reverse reactions are significantly suppressed by benefiting from the spatial separation of the oxidation (+2.21 V) and reduction (-1.19 V) regions. The homojunction exhibits efficient photocatalytic activity for H2 and O2 evolution (1270.5 and 36.0 μmol h−1) with the scavenger. Meanwhile, the solar-to-hydrogen efficiency of overall water splitting was improved to 0.14%. This research provides a new way for semiconductor design in solar energy conversion applications.

Niobium-Incorporated CoSe2 Nanothorns with Electronic Structural Alterations for Efficient Alkaline Oxygen Evolution Reaction at High Current Density.

Developing cost-effective, highly active, and robust electrocatalysts for oxygen evolution reaction (OER) at high current density is a critical challenge in water electrolysis since the sluggish kinetics of the OER significantly impedes the energy conversion efficiency of overall water splitting. Here, a 1D nanothorn-like Nb-CoSe2 /CC (CC=carbon cloth) structure was developed as an efficient OER catalyst. The optimized Nb-CoSe2 /CC catalyst exhibited remarkable OER performance with the low overpotentials of 220 mV at 10 mA cm-2 and 297 mV 200 mA cm-2 and a small Tafel slope (54.1 mV dec-1 ) in 1.0 m KOH electrolyte. More importantly, the Nb-CoSe2 /CC electrode displayed superior stability after 60 h of continuous operation. In addition, cell voltages of 1.52 and 1.93 V were required to achieve 10 and 500 mA cm-2 for the electrolyzer made of Nb-CoSe2 /CC (anode) and the Pt/C (cathode). Density functional theory (DFT) calculations combined with experimental results revealed that incorporating niobium into the CoSe2 could optimize the adsorption free energy of the reaction intermediates and enhance the conductivity to improve the catalytic activity further. Additionally, the super-hydrophilicity of Nb-CoSe2 /CC resulting from the surface defects increased the surface wettability and facilitated reaction kinetics. These results indicate that Nb-CoSe2 /CC intrinsically enhances OER performance and possesses potential practical water electrolysis applications.

Bifunctional integrated electrode for high-efficient hydrogen production coupled with 5-hydroxymethylfurfural oxidation

The sluggish oxygen evolution reaction (OER) limits the efficiency of overall water splitting, which thereby hinders hydrogen evolution reaction (HER). Here, we demonstrate a bifunctional CoNiP nanosheet integrated electrode (CoNiP-NIE) to boost HER and replace OER by 5-hydroxymethylfurfural oxidation reaction (HMFOR) to obtain high-valued 2,5-furandicarboxylic acid (FDCA). The as-developed CoNiP-NIE exhibits a constant high Faradaic efficiency more than 82% for HMFOR in a wide potential from 1.40 V to 1.70 V vs. RHE, which stand at the top level among the reported electrocatalysts. Moreover, the low overpotential for HER further indicates its high efficiency in the H2 generation. Based on the bifunctional activity of CoNiP, an electrochemical hydrogen evolution coupled with biomass oxidation device is constructed, which delivers lower voltage (1.46 V) for anode oxidation and higher evolution rate of H2 (41.2 L h−1 m−2) than water splitting (1.76 V, 16.1 L h−1 m−2).

Optimizing local charge distribution of metal nodes in bimetallic metal–organic frameworks for efficient urea oxidation reaction

A significantly lower voltage was required in NiFe-MIL-53-NH 2 when using full urea electrolysis instead of overall water splitting. • Incorporating Fe induces the formation of electrophilic Ni 3+ and nucleophilic Fe 3+ . • The bimetallic NiFe-MIL-53-NH 2 presents excellent electrocatalytic UOR activity. • This work provides a new strategy to explore effective UOR electrocatalysts. Electrocatalytic urea oxidation reaction (UOR) presents lower thermodynamic potential than oxygen evolution reaction (OER), thus exhibiting promising potential to enhance the efficiency of overall water splitting. However, due to the intrinsically sluggish six-electron transfer process, the efficiency of UOR is still not satisfied. In response, we synthesized a bimetallic NiFe-MIL-53-NH 2 with superior activity toward UOR, which only needs a low potential of 1.398 V vs. RHE to obtain 50 mA cm −2 in 1.0 M KOH with 0.33 M urea, much lower than that in 1.0 M KOH (1.721 V vs. RHE). Furthermore, NiFe-MIL-53-NH 2 presents significantly more excellent UOR activity compared to its monometallic counterparts. The TOF value in NiFe-MIL-53-NH 2 (0.16 s −1 ) at 1.4 V vs. RHE is about 133- and 246-folds higher than that Ni-MIL-53-NH 2 (1.2 × 10 -3 s −1 ) and Fe-MIL-53-NH 2 (6.5 × 10 -4 s −1 ), respectively. XPS characterization discloses that the incorporation of Fe into Ni-MIL-53-NH 2 framework optimizes the local charge distribution of metal nodes, leading to the formation of electrophilic Ni 3+ and nucleophilic Fe 3+ species, which can absorb electron-donating –NH 2 and electron-withdrawing C = O groups in urea, respectively, and therefore result in excellent UOR. This simple strategy of regulating local charge distribution of active species by fabricating bimetallic MOFs provides a new strategy and direction to explore other highly efficient UOR electrocatalysts.

Designing highly efficient 3D porous Ni-Fe sulfide nanosheets based catalyst for the overall water splitting through component regulation

Constructing efficient and stable bifunctional catalysts is essential to improve the conversion efficiency of overall water splitting (OWS). In this work, 3D porous Ni-Fe sulfide nanosheets supported on nickel foam (Ni-Fe-S/NF) were synthesized by a facile hydrothermal method. The optimized Ni3S2-FeS/NF-2 electrode realized ultra-high efficiency for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Benefiting from the unique 3D porous nanosheets structure and the strong electronic interactions between Ni3S2 and FeS through component regulation, low overpotentials of 253 and 262 mV are required to drive a current density of 100 mA cm−2 for OER and HER, respectively. Importantly, Ni3S2-FeS/NF-2 bifunctional catalyst only needs 1.55 and 1.75 V at 10 and 100 mA cm−2 respectively and works continuously for at least 100 h. The work thus provides an extraordinary promising catalyst for OWS and can be envisioned of potential for large-scale applications.

MOF-derived NiCoZnP nanoclusters anchored on hierarchical N-doped carbon nanosheets array as bifunctional electrocatalysts for overall water splitting

The development of novel bifunctional electrocatalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is urgently desired for improving the efficiency of overall water splitting but remains a great challenge. Herein, a metal–organic frameworks (MOFs)-derived hybrid nanostructure consisted of multiple transition metal phosphide (NiCoZnP) nanoclusters and hierarchical ultrathin N-doped carbon (NC) nanosheets is successfully synthesized as binder-free bifunctional electrocatalysts for overall water splitting. The ultrafine and monodispersed NiCoZnP nanoclusters with uniform sizes of 3 nm are homogeneously distributed on the ultrathin NC nanosheets, leading to self-supported NiCoZnP/NC nanosheets array on carbon cloth (CC). The NiCoZnP/NC exhibits large surface area and numerous active sites due to the small sizes of NiCoZnP and hierarchical nanostructures of NC. Furthermore, the NiCoZnP/NC nanosheets are directly grown on CC and avoids the usage of binder, which significantly reduces the electrical contact resistance and exhibits superhydrophilic performance. Therefore, the self-supported NiCoZnP/NC nanosheets array demonstrates high HER activity with low overpotential of 74 mV and OER activity with overpotential of 228 mV to reach current density of 10 mA cm−2 in 1.0 M KOH solution, and exhibits remarkable overall water splitting performances with low potential of 1.54 V to drive 10 mA cm−2 and good long-term stability.

Self-supported Co/CoO anchored on N-doped carbon composite as bifunctional electrocatalyst for efficient overall water splitting

Designing a non-noble metal-based bifunctional electrocatalyst for simultaneously boosting both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is highly desirable, which is decisive for enhancing the efficiency of overall water splitting. Herein, inspired by the appropriate H atoms binding energy of Co metal, favorable OER reaction kinetics of cobalt oxides, and more efficient electron transfer of self-supported structure, Co/CoO anchored on N-doped carbon layer coated on carbon cloth (Co/CoO@NC@CC) is synthesized by a facile self-assembly-carbonization method. Remarkably, the Co/CoO@NC@CC exhibits much increased electrochemical activities toward both OER and HER with low overpotentials of 284 and 152 mV required to deliver the current density of 10 mA cm−2, respectively, which are superior to most of the reported Co-based and CoO-based catalysts. More importantly, the fabricated Co/CoO@NC@CC‖ Co/CoO@NC@CC electrolyzer only needs a small cell voltage of 1.66 V for driving overall water splitting to achieve the current density of 10 mA cm−2. Moreover, the Co/CoO@NC@CC behaves superior stability after 25 h of continuous operation. Excellent features including the synergistic effect between Co and CoO, unique hierarchical porous structure, and self-supported construction jointly impart Co/CoO@NC@CC highly elevated bifunctional electrocatalytic activities.

One-Step Electrodeposition Synthesis of Bimetal Fe- and Co-Doped NiPi/P for Highly Efficient Overall Water Splitting

To improve the electrolysis efficiency of overall water splitting, designing an efficient and stable catalyst becomes very essential. Herein, a one-step cyclic voltammetric electrodeposition method...

Hierarchical MnCo2O4 nanowire@NiFe layered double hydroxide nanosheet heterostructures on Ni foam for overall water splitting

It is of great importance to construct non-precious metal bifunctional electrocatalysts with low cost and high efficiency for overall water splitting.

Nanoboxes endow non-noble-metal-based electrocatalysts with high efficiency for overall water splitting

Non-noble-metal nanoboxes with abundant surface active sites, facilitated electron/mass transport, favorable synergistic effects and electronic effects, serving as promising candidate materials for boosting electrochemical water splitting.

Superhydrophilic 3D peony flower-like Mo-doped Ni2S3@NiFe LDH heterostructure electrocatalyst for accelerating water splitting

Constructing highly efficient nonprecious electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is essential to improve the efficiency of overall water splitting, but still remains lots of obstacles. Herein, a novel 3D peony flower-like electrocatalyst was synthesized by employing Mo–Ni2S3/NF nanorod arrays as scaffolds to in situ growth ultrathin NiFe LDH nanosheets (Mo-Ni2S3@NiFe LDH). As expected, the novel peony flower-like Mo–Ni2S3@NiFe LDH displays superior electrocatalytic activity and stability for both OER and HER in alkaline media. Low overpotentials of only 228 mV and 109 mV are required to achieve the current densities of 50 mA cm−2 and 10 mA cm−2 for OER and HER, respectively. Additionally, the material remarkably accelerates water splitting with a low voltage of 1.54 V at 10 mA cm−2, which outperforms most transition metal electrodes. The outstanding electrocatalytic activity benefits from the following these features: 3D peony flower-like structure with rough surface provides more accessible active sites; superhydrophilic surfaces lead to the tight affinity between electrode with electrolyte; metallic Ni substrate and highly conductive Mo–Ni2S3 nanorods scaffold together with offer fast electron transfer; the nanorod arrays and porous Ni foam accelerate gas bubble release and ions transmission; the strong interfacial effect between Mo-doped Ni3S2 and NiFe LDH shortens transport pathway, which are benefit for electrocatalytic performance enhancement. This work paves a new avenue for construction and fabrication the 3D porous structure to boost the intrinsic catalytic activities for energy conversion and storage applications.

Enhancing visible-light photocatalytic activity for overall water splitting in UiO-66 by controlling metal node composition

The photocatalytic activity of a series of five UiO-66 (M: Zr, Zr/Ti, Zr/Ce, Zr/Ce/Ti, Ce) materials for overall water splitting with generation of hydrogen and oxygen has been herein measured. The most efficient photocatalyst for the overall water splitting is the trimetallic MOF UiO-66(Zr/Ce/Ti) which achieves 230 μ mol ∙ g−1 of H2 and 110 μ mol ∙ g−1 of O2, upon UV light irradiation, and 210 μ mol ∙ g−1 of H2 and 70 μ mol ∙ g−1 of O2, under visible light irradiation. These productivity data indicate that a considerable percentage of its photocatalytic activity derives from the visible region of the spectrum (λ > 450 nm). The photocatalytic activity of trimetallic UiO-66(Zr/Ce/Ti) was maintained upon reuse. Kinetics of the charge separated state monitored by transient absorption spectroscopy shows similar deactivation profiles for the five UiO-66 samples, suggesting that it is the charge separation efficiency the main factor responsible for the differences in the photocatalytic activity. The use of methanol as sacrificial agent during the photocatalytic experiments indicated that the high photocatalytic efficiency for overall water splitting in UiO-66(Zr/Ce/Ti) derives from the favorable kinetics of oxygen evolution. These results show the potential of multimetallic metal-organic frameworks as solar photocatalysts by tuning light absorption towards the visible region.