Lanthanum doped copper oxide nanoparticles enabled proficient bi-functional electrocatalyst for overall water splitting

The need for a clean and an environmentally non-degrading sustainable energy resource has grown worldwide due to the huge depletion of other fuel sources, as a result, production of hydrogen by electrochemical water splitting is considered as a potential answer to this pertaining need. However, development of low-cost electrocatalyst as a replacement for Pt and RuO₂ for both Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) remains a significant challenge for the production of hydrogen at a larger scale. This study presents the synthesis of non-noble metal-based lanthanum doped copper oxide nanoparticles as a potential bi-functional electrocatalyst for overall water splitting in alkaline electrolyte. The optimized 1% lanthanum (La) doped CuO electrocatalyst exhibits outstanding OER and HER activity in 1.0 M KOH electrolyte posting a potential of 1.552 V vs RHE for OER and −0.173 V vs RHE for HER at a current density of ~10 mAcm⁻². Significantly, the functional bi-catalyst exhibits a low cell voltage of 1.6 V to achieve overall water splitting at a current density of 10 mAcm⁻² along with long-term stability of 13.5 h for a cell voltage of 2.25 V at a constant current density of 30 mAcm⁻² with only 20% initial current lose after 13.5 h. The results demonstrate that the incorporation of the rare-earth element onto CuO nanoparticles has made it a viable high-end non-noble electrocatalyst for overall water splitting.     

Highly-stable,bifunctional, binder-free & stand-alone photoelectrode (FexNi1-xO@a-CC) for natural waters splitting into hydrogen

Photoelectrochemical (PEC) water splitting is a promising approach to boost green hydrogen production. Herein, we prepared novel binder-free photoelectrode by direct growth of iron doped nickel oxide catalyst over activated carbon cloth (Fe_xNi_1-xO@a-CC) having band gap energy of 2.2 eV for overall water splitting. Fe_xNi_1-xO@a-CC photoelectrode had shown remarkable lower potential of only 1.36 V for oxygen evolution reaction (OER) to reach 10 mA cm^?2 current density using very low photonic intensity of 8.36 × 10^?4 E/L.s. For the first time, we also reported electrical efficiency required for PEC water splitting for 1 m³ of water that is equal to 0.09 kWh/m³. Fe_xNi_1-xO@a-CC photoelectrode also exhibits low potentials of 1.44 V (OER) and ?0.210 V (HER) at 10 mA cm^?2 to split sea water. Our results confirmed that designing Fe_xNi_1-xO@a-CC photoelectrode would be an innovative step to widen green energy conversion applications using natural waters (both sea and fresh water).     

Electrodeposited Ni-Co-Sn alloy as a highly efficient electrocatalyst for water splitting

Water splitting to produce hydrogen and oxygen is considered as a feasible solution to solve the current energy crisis. It is highly desirable to develop inexpensive and efficient electrocatalyst for both the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). In this paper, nanostructured Ni-Co-Sn alloys were electrodeposited on copper foil and the excellent electrocatalytic performances for both HER and OER in alkaline media were achieved. The optimized Ni-Co-Sn electrode shows a low onset overpotential of −18 mV and a small Tafel slope of 63 mV/dec for the HER, comparable to many state-of-the-art non-precious metal HER catalysts. For the OER, it produces an overpotential of 270 mV (1.50 V vs. RHE) at current density of 10 mA/cm², which is better than that of the commercial Ir/C catalyst. In addition to high electrocatalytic activities, it exhibits good stability for both HER and OER. This is the first report that Ni-Co-Sn is served as a cost-effective and highly efficient bifunctional catalyst for water splitting and it will be of great practical value.     

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

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

Combustion-derived BaNiO3 nanoparticles as a potential bifunctional electrocatalyst for overall water splitting

Electrochemical water electrolyser though an assuring solution for clean hydrogen production, the sluggish kinetics and high cost of existing precious metal electrocatalyst remains a barrier to its effective utilization. Herein, solution combustion route derived perovskite type barium nickelate (BaNiO₃) nanoparticles were developed and studied for their bifunctional electrocatalytic properties towards overall water splitting. The unannealed BaNiO₃ nanoparticles exhibited the highest OER and HER activity with overpotentials 253 mV and 427 mV respectively to attain 10 mAcm⁻² in 1.0 M KOH. Using unannealed BaNiO₃ as a bifunctional electrocatalyst in a two-electrode alkaline electrolyser, the cell was able to achieve the benchmark current density at a low cell voltage of 1.82 V. Impressively the setup's electrocatalytic performance improved 4.9% after continuous overall water splitting for 24 h at 30 mAcm⁻². Therefore, BaNiO₃ nanoparticles can be a low-cost and efficient alternative for noble metal electrocatalysts for clean H₂ production.     

Hydrothermally synthesized nickel molybdenum selenide composites as cost-effective and efficient trifunctional electrocatalysts for water splitting reactions

The development of efficient, cost-effective routes to prepare non-platinum-based electrocatalysts is a significant scientific challenge in water-splitting systems. A multifunctional electrocatalyst for the hydrogen evolution, oxygen evolution, and oxygen reduction reactions (HER/OER/ORR) involved in the water-splitting process was fabricated using a simple and eco-friendly strategy. The present study involves the simple synthesis of nanostructured nickel selenide (NiSe) via a hydrothermal method. The different phases of nickel selenide and their dependency on the precursor concentration were analyzed using X-ray diffraction (XRD). The morphologies of coral-like structured pure and Mo-doped NiSe (Ni_1-xMo_xSe) samples were investigated systematically using scanning electron microscopy (SEM). The as-prepared Ni_0.5Mo_0.5Se material showed an enhanced electrochemical activity of 1.57 V @ 10 mA/cm² for OER and 0.19 V @ 10 mA/cm² to HER, and follows the Volmer-Heyrovsky for HER mechanism. In addition, the electrocatalyst exhibits a large electrochemical surface area and high stability. Therefore, the hydrothermally synthesized Ni_1–xMo_xSe has been proven to be a perfect platinum-free trifunctional electrocatalyst for water splitting process.     

Bifunctional electrocatalysts for water splitting from a bimetallic (V doped-NixFey) Metal–Organic framework MOF@Graphene oxide composite

An ongoing challenge still lies in the exploration of proficient electrocatalysts from earth-abundant non-precious metals instead of noble metal-based catalysts for clean hydrogen energy through large-Scale electrochemical water splitting. However, developing a non-precious transition metals based, stable electrocatalyst for cathodic hydrogen evolution reaction (HER) and anodic oxygen evolution reaction (OER) is important challenge for modern energy conversion technology. In this report Vanadium doped bimetallic nickel-iron nanoarray, fabricated by carbon supported architecture through carbonization process for electrochemical water splitting. Three types of catalysts were prepared in different molar ratio of Ni/Fe. The electrocatalytic performance demonstrated that the catalyst with equal mole ratio (0.06:0.06) of Ni/Fe possess high catalytic activity for both OER and HER in alkaline and acidic medium. Besides, our findings revealed that the doping of vanadium could play a strong synergetic effect with Ni/Fe, which provide a small overpotential of 90 mV and 210 mV at 10 mA cm^?2 for HER and OER respectively compared to the other two catalyst counterparts. Also, the catalyst with 1:1 (Ni/Fe) molar ratio showed a high current density of 208 mA cm^?2 for HER at 0.5 M H₂SO₄ and 579 mA cm^?2 for OER at 1 M KOH solution, the both current densities are much higher than the other two catalysts (different Ni/Fe ratio). In addition, the presented catalysts showed extremely good durability, reflecting in more than 20 h of consistent Chronoamprometry study at fixed overpotential η = 250 mV without any visible voltage elevation. Similarly, the (Ni/Fe) equal ratio catalyst showed better corrosion potential 0.209 V vs Ag/AgCl and lower current density 0.594 × 10^?12 A cm^?2 in high alkaline medium. The V-doping, MOF/GO surface defects are significantly increased the corrosion potential of the V-Ni_xFe_y-MOF/GO electrocatalyst. Besides, the water electrolyzed products were analysed by gas chromatography to get clear insights on the formed H₂ and O₂ products.     

Autogenous growth of highly active bifunctional Ni–Fe2B nanosheet arrays toward efficient overall water splitting

Developing an effective and low-cost bifunctional electrocatalyst for both OER and HER to achieve overall water splitting is remaining a challenge to meet the needs of sustainable development. Herein, an electroless plating method was employed to autogenous growth of ultrathin Ni–Fe₂B nanosheet arrays on nickel foam (NF), in which the whole liquid phase reduction reaction took no more than 20 min and did not require any other treatments such as calcination. In 1.0 M KOH electrolyte, the resulted Ni–Fe₂B ultrathin nanosheet displayed a low overpotential of 250 mV for OER and 115 mV for HER to deliver a current density of 10 mA cm^?2, and both OER and HER activities remained stable after 26 h stability testing. Further, the couple electrodes composed of Ni–Fe₂B could afford a current density of 10 mA cm^?2 towards overall water splitting at a cell voltage of 1.64 V in 1.0 M KOH and along with excellent stability for 26 h. The outstanding electrocatalytic activities can be attributed to the synergistic effect of electron-coupling across Ni and Fe atoms and active sites exposed by large surface area. The effective combination of low cost and high electrocatalytic activity brings about a promising prospect for Ni–Fe₂B nanosheet arrays in the field of overall water splitting.     

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

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

Flower-like HEA/MoS2/MoP heterostructure based on interface engineering for efficient overall water splitting

The development of cheap, efficient, and active non-noble metal electrocatalysts for total hydrolysis of water (oxygen evolution reaction (OER) and hydrogen evolution reaction (HER)) is of great significance to promote the application of water splitting. Herein, a heterogeneous structured electrode based on FeAlCrMoV high-entropy alloy (HEA) was synthesized as a cost-effective electrocatalyst for hydrogen and oxygen evolution reactions in alkaline media. In combination of the interfacial synergistic effect and the high-entropy coordination environment, flower-like HEA/MoS₂/MoP exhibited the excellent HER and OER electrocatalytic performance. It showed a low overpotential of 230 mV at the current density of 10 mA cm⁻² for OER and 148 mV for HER in alkaline electrolyte, respectively. Furthermore, HEA/MoS₂/MoP as both anode and cathode also exhibited an overpotential of 1.60 V for overall water splitting. This work provides a new strategy for heterogeneous structure construction and overall water splitting based on high-entropy alloys.     

High throughput preparation of Ni–Mo alloy thin films as efficient bifunctional electrocatalysts for water splitting

The synthesis of cost-effective and high-performance electrocatalysts for water splitting is the main challenge in electrochemical hydrogen production. In this study, we adopted a high throughput method to prepare bi-metallic catalysts for oxygen/hydrogen evolution reactions (OER/HER). A series of Ni–Mo alloy electrocatalysts with tunable compositions were prepared by a simple co-sputtering method. Due to the synergistic effect between Ni and Mo, the intrinsic electrocatalytic activity of the Ni–Mo alloy electrocatalysts is improved, resulting in excellent HER and OER performances. The Ni₉₀Mo₁₀ electrocatalyst shows the best HER performance, with an extremely low overpotential of 58 mV at 10 mA cm^?2, while the Ni₄₀Mo₆₀ electrocatalyst shows an overpotential of 258 mV at 10 mA cm^?2 in OER. More significantly, the assembled Ni₄₀Mo₆₀//Ni₉₀Mo₁₀ electrolyzer only needs a cell voltage of 1.57 V to reach 10 mA cm^?2 for overall water splitting.     

An efficient Fe2O3/FeS heterostructures water oxidation catalyst

Slow kinetics and insufficient understanding of the perceptual design of oxygen evolution reaction (OER) electrocatalysts are major obstacles. Overcoming these challenges, heterostructures have recently attracted attention because they encourage alternative OER electrocatalysts with active structural features. In this study, synthesis, characterization and electrochemical evaluation of the heterostructure of iron oxide/iron sulfide (Fe₂O₃/FeS) and its counterparts, iron oxide (Fe₂O₃) and iron sulfide (FeS) are reported. The structural features of as-synthesized electrocatalysts have been evaluated by infrared spectroscopy, powder X-ray diffraction study and scanning electron microscopy. Fe₂O₃/FeS was found to be a stable electrocatalyst for efficient water splitting, which initiates OER at a surprisingly low potential of 1.49 V (vs RHE) in 1 M potassium hydroxide. The Fe₂O₃/FeS electrocatalyst drives OER with a current density of 40 mA cm^?2 at overpotential of 370 mV and a Tafel slope of 90 mV dec^?1. Its performance is better than its counterparts (Fe₂O₃ and FeS) under similar electrochemical conditions. At an applied potential of 1.65 V (vs RHE), continuous oxygen production for several hours revealed the long-term stability and effective activity of the Fe₂O₃/FeS electrocatalyst for OER. The as-developed Fe₂O₃/FeS heterostructure provides an effective alternative low-cost metal-based electrocatalysts for OER.     

A novel in-situ strategy develops for Mo2C nanoparticles incorporated on N,P co-doped stereotaxically carbon as efficient electrocatalyst for overall water splitting

Developing cost-effective and remarkable electrocatalysts toward oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) performs excelling role in boosting the hydrogen energy application. Herein, a novel in-situ one-pot strategy is developed for the first time to synthesize molybdenum carbide nanoparticles (Mo₂C NPs) incorporated on nitrogen (N) and phosphorous (P) co-doped stereotaxically carbon (SC). The optimized Mo₂C NPs/N, P–SC–800 electrocatalyst exhibits lower overpotentials of 131 and 287 mV for HER and OER to deliver a current density of 10 mA cm^?2 in 1.0 M KOH medium with smaller Tafel slopes of 58.9 and 74.4 mV/dec, respectively. In addition, an electrolyzer using Mo₂C NPs/N, P–SC–800 electrode as cathode and anode delivers a current density of 10 mA cm^?2 at a small voltage of 1.64 V for overall water splitting. The excellent water splitting performance could be ascribed to optimum Mo₂C NPs for more accessible active sites, highly active N, P-SC networks for accelerated electron transfers, and synergetic effect between Mo₂C NPs and N, P-SC networks. The N, P-SC network not only enhances the overall dispersion of Mo₂C NPs but also contributes numerous electroactive edges to enhance the performance of HER, OER, and overall water splitting activity. This research work explores the in-situ one-step strategies of advanced, cost-effective, and non-precious metal electrocatalysts for efficient water splitting and motivates the consideration of a novel class of heteroatom doped stereotaxically carbon nanocomposites for sustainable energy production.     

Bimetallic metal-organic framework derived electrocatalyst for efficient overall water splitting

The development of bifunctional catalysts that can be applied to both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is widely regarded as a key factor in the production of sustainable hydrogen fuel by electrochemical water splitting. In this work, we present a high-performance electrocatalyst based on nickel-cobalt metal-organic frameworks for overall water splitting. The as-obtained catalyst shows low overpotential to reaches the current density of 10 mA cm⁻² with 249 mV for OER and 143 mV for HER in alkaline media, respectively. More importantly, when the electrolyzer was assembled with the as-prepared catalyst as anode and cathode simultaneously, it demonstrates excellent activity just applies a potential of 1.68 V to achieve 10 mA cm⁻² current density for overall water splitting.     

Efficient CoMoRu0.25Ox/NF nanoplate architectures for overall electrochemical water splitting

The development of inexpensive electrocatalysts with excellent electrocatalytic activity for the hydrogen and oxygen evolution reactions (HER and OER, respectively) has been challenging. In this study, we synthesized cobalt molybdenum ruthenium oxide with porous, loosely-assembled nanoplate morphology. The CoMoRu_0.25O_x/NF electrocatalyst exhibited the highest electrocatalytic activity, requiring overpotentials of 230 and 78 mV for the OER and HER, respectively, to attain a current density of 10 mA cm^?2; moreover, its long-term stability was outstanding. The electrocatalyst required a cell voltage of only 1.51 V for overall water splitting in an alkaline medium, which was lower than that required by many CoMo-based catalysts.     

Transition metal carbides coupled with nitrogen-doped carbon as efficient and stable Bi-functional catalysts for oxygen reduction reaction and hydrogen evolution reaction

Developing non-precious metal catalysts for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) is crucial for proton exchange membrane fuel cell (PEMFC), metal-air batteries and water splitting. Here, we report a in-situ simple approach to synthesize ultra-small sized transition metal carbides (TMCs) nanoparticles coupled with nitrogen-doped carbon hybrids (TMCs/NC, including WC/NC, V₈C₇/NC and Mo₂C/NC). The TMCs/NC exhibit excellent ORR and HER performances in acidic electrolyte as bi-functional catalysts. The potential of WC/NC at the current density of 3.0 mA cm^?2 for ORR is 0.814 V (vs. reversible hydrogen electrode (RHE)), which is very close to Pt/C (0.827 V), making it one of the best TMCs based ORR catalysts in acidic electrolyte. Besides, the TMCs/NC exhibit excellent performances toward HER, the Mo₂C/NC only need an overpotential of 80 mV to drive the current density of 10 mA cm^?2, which is very close to Pt/C (37 mV), making it the competitive alternative candidate among the reported non-precious metal HER catalysts.     

Efficient bifunctional hydrogen and oxygen evolution reaction electrocatalyst based on the NU-1000/CuCo2S4 heterojunction

One of the current necessities to produce clean energy is the logical design of inexpensive noble-metal free electrocatalysts with developed structure and composition for electrochemical water splitting. In this study, we introduce a new core-shell-structured bifunctional electrocatalyst of NU-1000/CuCo₂S₄ for oxygen evolution reaction (OER), hydrogen evolution reaction (HER) and overall water splitting for the first time. Own to unique structure with rich porosity, high electrical conductivity, high stability and larger density of active sites, this nanocomposite can produce water electrolysis in a 1 M KOH solution. The electrochemical measurements show overpotentials of 335 mV for OER and 93 mV for HER at a current density of 10 mAcm⁻². Also, the NU-1000/CuCo₂S₄ nanocomposite exhibits Tafel slope values of 110 mV dec⁻¹ and 103 mV dec⁻¹ for HER and OER, respectively. Besides, NU-1000/CuCo₂S₄ presents a significant long-term stability in a 72 h run. Additionally, NU-1000/CuCo₂S₄ requires 1.55 V to deliver 10 mA cm⁻² current density in overall water splitting. According to these results, we hope to use this electrocatalyst in producing oxygen and hydrogen from water.     

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.     

Bifunctional nanoporous ruthenium-nickel alloy nanowire electrocatalysts towards oxygen/hydrogen evolution reaction

A class of ruthenium-nickel alloy catalysts featured with nanoporous nanowires (NPNWs) were synthesized by a strategy combining rapid solidification with two-step dealloying. RuNi NPNWs exhibit excellent electrocatalytic activity and stability for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in which the RuNi-2500 NPNWs catalyst shows an OER overpotential of 327 mV to deliver a current density of 10 mA cm^?2 and the RuNi-0 NPNWs catalyst requires the overpotential of 69 mV at 10 mA cm^?2 showing the best HER activity in alkaline media. Moreover, the RuNi-1500 NPNWs catalyst was used as the bifunctional electrocatalyst in a two-electrode alkaline electrolyzer for water splitting, which exhibits a low cell voltage of 1.553 V and a long-term stability of 24 h at 10 mA cm^?2, demonstrating that the RuNi NPNWs catalysts can be considered as promising bifunctional alkaline electrocatalysts.     

Uniform cobalt nanoparticles embedded in nitrogen-doped graphene with abundant defects as high-performance bifunctional electrocatalyst in overall water splitting

Co nanoparticles with uniform size (about 5 nm) embedded in N-doped graphene (Co-NG) were explored in this work. The introduction of a second carbon source of citric acid during synthesis prevented the Co atoms from growing up, thus regulating the size of the cobalt nanoparticles. N atoms in N-doped graphene had more lone-pair electrons, making it easier to capture electrons from hydrated ions, and facilitating the dynamics procedure of HER. Furthermore, N dopant rendered larger positive charge density on the adjacent carbon atoms, which was conducive to OER and HER. At 10 mA cm^?2 of the current density, the Co-NG/CC catalyst's overvoltage of HER was 78 mV, approaching that of 20% Pt/C (59 mV), an efficient precious metal electrocatalyst for HER, while its overvoltage of OER was about 225 mV, 12.5% lower than that of RuO₂ (257 mV, a common precious metal oxide OER electrocatalyst). In addition, this Co-NG/CC composite bifunctional catalyst displayed good electrochemical stability in alkali solution and might be designed as a dual-function catalyst in the application of overall water splitting. The cell voltage of Co-NG/CC//Co-NG/CC was only 1.66 V, approaching to that of full precious metal cell of Pt/C//RuO₂ (1.52 V), and revealing the good commercial application prospects of this composite bifunctional catalyst.