P doped NiCoZn LDH growth on nickel foam as an highly efficient bifunctional electrocatalyst for Overall Urea-Water Electrolysis

Water electrolysis is one of the important methods for hydrogen production, but the oxygen evolution reaction (OER) on the anode has a higher theoretical potential. Using urea oxidation reaction (UOR) instead of OER has been an energy-saving method because it has a lower theoretical potential and also can reduce pollution. In this paper, NiCoZn LDH/NF, P–NiCoZn LDH/NF-X (X is the atom ratio of P) = 10%, 15%, 20%) were synthesized through typically hydrothermal and calcination methods. P–NiCoZn LDH/NF-15% was demonstrated to be abifunctional electrocatalyst towards HER and UOR. When P–NiCoZn LDH/NF-15% is used as the anode and cathode for urea-water electrolysis,it shows that when the current density is 100 mA cm^?2, the voltage is 1.479 V for urea-water electrolysis, which is much better than that of IrO₂/NF||Pt/C/NF (1.698 V). Thus, P–NiCoZn LDH/NF-15% is expected to replace precious metals for practical applications.     

Constructing rod-shaped Co2C/MoN as efficient bifunctional electrocatalyst towards overall urea-water electrolysis

In this paper, Co₂C/MoN/NF at different calcination temperatures (T = 500, 550, 600, 650, 700 °C) was prepared in situ on 3D foam nickel (NF) by hydrothermal treatment and high-temperature calcination. The experimental results show that the sample synthesized at 600 °C (Co₂C/MoN-600/NF) has the best catalytic capacity and the maximum electrochemical active area. For the hydrogen evolution reaction (HER), the potential is only ?176 mV at 100 mA cm^?2, meanwhile, only 1.42 V is needed for urea oxidation reaction (UOR). Furthermore, a two-electrode electrolyze cell of Co₂C/MoN-600/NF6Co₂C/MoN-600/NF was constructed. And the voltage required for overall urea splitting (OUS) is 1.507 V at 50 mA cm^?2, which is 171 mV lower than that of overall water splitting (OWS, 1.678 V). Moreover, the prepared catalyst not only can treat urea in wastewater but also catalyze the production of hydrogen. Therefore, it will be a promising green electrocatalyst.     

Self-assembly of Ni2P/CoSe2 heterostructure as bifunctional electrocatalysts for urea-water electrolysis

In this paper, M-Se-L (M = Co, Ni, Fe. L = Se At%) were synthesized by solvothermal method. The results from electrochemical testing showed that Co–Se-75% (CoSe₂) has the highest catalytic performance among all M-Se-L. Furthermore, Ni₂P was compounded with CoSe₂ to form a heterogeneous structure Ni₂P/CoSe₂/NF. And the temperature and quality of NaH₂PO₂ during the synthesis process were optimized. It was found that the Ni₂P/CoSe₂/NF synthesized at 300 °C with 1.2 g NaH₂PO₂ had better catalytic performance. Only 1.383 V is required for UOR to reach 100 mA cm^?2. In alkaline urea-water system, the electrolytic voltage of Ni₂P/CoSe₂/NF||Ni₂P/CoSe₂/NF dual-electrode electrolyzer 1.607 V required to reach 100 mA cm^?2. The present work shows that Ni₂P/CoSe₂/NF is an efficient bifunctional electrocatalyst with good prospects for industry applications.     

NiFe-LDH/MWCNTs/NF nanohybrids as a high-performance bifunctional electrocatalyst for overall urea electrolysis

It is crucial for the storage and conversion of hydrogen energy to substitute the low theoretical potential of urea oxidation reaction (UOR) for the high theoretical potential of anodic water electrolysis (oxygen evolution reaction (OER)). In this paper, it puts forward a brief and scalable strategy, so as to synthesize a novel bifunctional nickel-iron layered double hydroxide and multi-walled carbon nanotube composites supported on Ni foam, represented as NiFe-LDH/MWCNTs/NF. Electrochemical measurements demonstrate that NiFe-LDH/MWCNTs/NF is able to realize an efficient electrocatalysis for UOR. During this process, merely a potential of 1.335 V is needed at 10 mA cm⁻², which can be taken to replace OER, thus reducing overpotential in H₂-production as well as power consumption. In addition, NiFe-LDH/MWCNTs/NF also exhibits electro-defense electrocatalytic efficiency to achieve the reaction of hydrogen evolving process, which provides a low overpotential of 98 mV at 10 mA cm⁻². To further prove it, all-water-urea electrolysis measurement is carried out in 1 M KOH and 0.5 M Urea with NiFe-LDH/MWCNTs/NF as cathode and anode respectively. NiFe-LDH/MWCNTs/NF||NiFe-LDH/MWCNTs/NF electrode manages to provide 10 mA cm⁻² at a voltage of merely 1.507 V, 156 mV lower than that of water splitting, which proves its commercial viability in energy-saving hydrogen production.     

Nanoengineered Zn-modified Nickel Sulfide (NiS) as a bifunctional electrocatalyst for overall water splitting

Developing an efficient and inexpensive electrocatalyst is of paramount importance for realizing the green hydrogen economy through electrocatalytic water splitting. Here, we demonstrated a facile large-scale, industrially viable binder-free synthesis of Zn-doped NiS electrocatalyst on bare nickel foam (NF) through a hydrothermal technique. The present catalyst, i.e., nickel sulfide (NiS) nanosheets on nickel foam with optimized doping of Zn atom (Zn–NiS-3), displays excellent catalytic efficacy for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). It requires an overpotential of 320 mV for OER at a current density of 50 mA cm⁻² and an overpotential of 208 mV for HER at a current density of 10 mA cm⁻². The water electrolyser device having Zn–NiS-3 electrocatalyst as both cathode and anode show excellent performance, requiring a cell voltage of only 1.71 V to reach a current density of 10 mA cm⁻² in an alkaline media. The density functional theory (DFT) based calculations showed enhanced density of states near Fermi energy after Zn doping in NiS and attributed to the enhanced catalytic activities. Thus, the present study demonstrates that Zn–NiS-3@NF can be coined as a viable electrocatalyst for green hydrogen production.     

Mo/P doped NiFeSe as bifunctional electrocatalysts for overall water splitting

Designing high-efficiency catalysts for overall water splitting is critical to reduce the cost of hydrogen fuel as a clean and renewable energy source in future society. In this work, a Mo-, P-codoped NiFeSe was successfully synthesized on nickel foam (NF) by one-step electrodeposition. Through the doping strategy, the conductivity can be well promoted, and the production of nanosheets on the catalyst surface and active phases during hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) provided much more active sites, which leaded to efficient HER/OER performances of as-synthesized Mo-, P-codoped NiFeSe catalysts, i.e., a low overpotential of 100 mV/200 mV at current density of 10 mA cm⁻² in 1.0 M KOH with stability of 95 h/60 h, respectively. It only required 1.53 V to deliver a current density of 10 mA cm⁻² in overall water splitting and maintained outstanding durability for 100 h. This work is beneficial to future design of high efficient and low-cost bifunctional catalysts for overall water splitting.     

(Fe,Ni)S2@MoS2/NiS2 hollow heterostructure nanocubes for high-performance alkaline water electrolysis

Hollow hybrid heterostructures are regarded to be promising materials as bifunctional electrocatalysts for highly efficient water electrolysis due to their intriguing morphological features and remarkable electrochemical properties. Herein, with FeNi-PBA as both a precursor and morphological template, we demonstrate the rational construct of cost-effective (Fe,Ni)S₂@MoS₂/NiS₂ hollow hybrid heterostructures as bifunctional electrocatalysts for alkaline overall water splitting. Microstructural analysis shows that the hybrid is a kind of hierarchical heterostructure composed of MoS₂/NiS₂ nanosheets/nanoparticles in situ grown on hollow (Fe,Ni)S₂ nanocubes with abundant heterointerfaces, which effectively maximizes the electrochemical active sites to the accessible electrolyte ions, leading to the promoted charge transfer. As expected, the hybrid shows remarkable alkaline electrocatalytic performance, such as hydrogen evolution overpotential of 176 mV and oxygen evolution overpotential of 342 mV at 50 mA cm^?2, as well a cell voltage of 1.65 V at 20 mA cm^?2. Moreover, the stability and durability are greatly enhanced under harsh electrochemical conditions. This study opens a new venue for developing earth-abundant bifunctional electrocatalysts with hollow hybrid heterostructures for alkaline water electrolysis in the future.     

Electrodeposition NiMoSe ternary nanoshperes on nickel foam as bifunctional electrocatalyst for urea electrolysis and hydrogen evolution reaction

Electrodeposition provides a simple but effective way to prepare advanced electrode for the application in electrochemical field. In this work, NiMoSe ternary nanospheres were deposited on nickel foam (NiMoSe/NF) by one-step electrodeposition. The morphology, phase and chemical composition of the electrode was characterized by using SEM, TEM, XRD and XPS. The electrode exhibited excellent performance for both urea oxidation reaction (UOR) and hydrogen evolution reaction (HER). It only required 1.39 V and 81 mV (vs. RHE) to deliver a current density of 10 mA/cm² for UOR and HER, respectively. The electrolyzer constructed with NiMoSe/NF as both anode and cathode could deliver a current density of 10 mA/cm² at a driving potential of 1.44 V. The stability test showed that the electrode had good durability as electrode for both UOR and HER. Considering the easiness, simplicity and low cost, the NiMoSe/NF electrode could find wide application in urea electrolysis.     

Co3Mo3N nanosheets arrays on nickel foam as highly efficient bifunctional electrocatalysts for overall urea electrolysis

Replacing dynamics-restricted oxygen evolution reaction (OER) with smart urea oxidation reaction (UOR) is very important for reducing the power consumption for hydrogen production. Here, the Co₃Mo₃N-400/NF is prepared using a facial way, which exhibits remarkable catalytic performances for UOR, hydrogen evolution reaction (HER) and overall urea electrolysis (OUE) because of the more exposed active sites and high electrical conductivity. At 100 mA/cm², the Co₃Mo₃N-400/NF shows a small potential of 1.356 V vs. RHE (reversible hydrogen electrode) for UOR, which is much lower than that for OER. Furthermore, for HER, to reach to 100 mA/cm², a low overpotential of 299 mV is required, and the urea has negligible influence on the HER process. For OUE, the Co₃Mo₃N-400/NF||Co₃Mo₃N-400/NF shows a small cell potential of 1.481 V at 100 mA/cm² along with a good durability. Our work provides more choice for future OUE to generate hydrogen.     

In situ formation of a nickel-iron-sulfur bifunctional catalyst within a porous polythiophene coating for water electrolysis

Developing readily scalable synthesis techniques for electrocatalysts is highly desirable for large-scale high-efficiency energy storage by water electrolysis. In this work, a coupled procedure of direct electrodeposition and in situ chemical transformation is presented to synthesize a nickel-iron-sulfur (Ni–Fe–S) composite catalyst. A polythiophene (PTh) coating with abundant micro/nano holes is directly deposited on graphite electrode at a constant potential. Two precursor solutions were injected onto and completely absorbed by the porous PTh coating, within which they spontaneously combine to form active species for catalysis. The PTh coating functions as a monolithic conductive matrix that well captures and disperses the catalyst species and thus decreases the contact resistance across the phase interfaces. The prepared catalyst shows a high catalytic performance for both hydrogen and oxygen evolution reactions. It requires a full cell voltage of about 2.0 V to afford a current density of 100 mA cm^?2 in 1.0 M KOH, with no activity degradation at least for 24 h. The active species for the cathodic and anodic catalysis are different and discussed separately. This work indicates that in situ chemical synthesis within a porous conductive polymer coating is a promising approach for preparing high efficiency electrocatalysts.     

Ultrathin MoS2 nanosheets in situ grown on rich defective Ni0.96S as heterojunction bifunctional electrocatalysts for alkaline water electrolysis

Developing earth-abundant and highly active bifunctional electrocatalysts are critical to advance sustainable hydrogen production via alkaline water electrolysis but still challenging. Herein, heterojunction hybrid of ultrathin molybdenum disulfide (MoS₂) nanosheets and non-stoichiometric nickel sulfide (Ni_0.96S) is in situ prepared via a facile one-step hydrothermal strategy, followed by annealing at 400 °C for 1 h. Microstructural analysis shows that the hybrid is composed of intimate heterojunction interfaces between Ni_0.96S and MoS₂ with exposed active edges provided by ultrathin MoS₂ nanosheets and rich defects provided by non-stoichiometric Ni_0.96S nanocrystals. As expected, it is evaluated as bifunctional electrocatalysts to produce both hydrogen and oxygen via water electrolysis with a hydrogen evolution reaction (HER) overpotential of 104 mV at 10 mA cm⁻² and an oxygen evolution reaction (OER) overpotential of 266 mV at 20 mA cm⁻² under alkaline conditions, outperforming most current noble-metal-free electrocatalysts. This work provides a simple strategy toward the rational design of novel heterojunction electrocatalysts which would be a promising candidate for electrochemical overall water splitting.     

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.     

Co-based MOF-derived Co/CoN/Co2P ternary composite embedded in N- and P-doped carbon as bifunctional nanocatalysts for efficient overall water splitting

In this work, we developed ternary metallic cobalt-cobalt nitride-dicobalt phosphide composite embedded in nitrogen and phosphorus co-doped carbon (Co/CoN/Co₂P-NPC) as bifunctional catalysts for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The as-prepared Co/CoN/Co₂P-NPC is achieved by simultaneous annealing and phosphating of a Co–N rich metal-organic frameworks (MOFs) precursor. Compare with the phosphorus-free Co/CoN embedded nitrogen-doped carbon electrocatalyst (Co/CoN-NC), the as-prepared Co/CoN/Co₂P-NPC display superior HER and OER low overpotential of 99 mV and 272 mV at current density of 10 mA cm⁻². When Co/CoN/Co₂P-NPC electrocatalyst is use as bifunctional catalysts in overall alkaline water splitting, it exhibit excellent behaviour with 10 mA cm⁻² current at overall cell potential of 1.60 V. The excellent performance of Co/CoN/Co₂P-NPC electrocatalyst is attributed to the phosphating process that could further enhance synergistic effect, create stronger electronic interactions, and form efficient dual heteroatom doping to optimize the interfacial adhesion within the electrocatalyst. This present work will create more opportunities for the development of new, promising and more active sites electrocatalysts for alkaline electrolysis.     

Facile construction of heterostructural Ni3(NO3)2(OH)4/CeO2 bifunctional catalysts for boosted overall water splitting

Interface engineering has aroused vitally widespread concern since it could be an effective strategy for exploring high-performance and low-cost water oxidation electrocatalysts. Herein, we report a hetero-structured Ni₃(NO₃)₂(OH)₄/CeO₂/NF (NNO/CeO₂/NF) electrode, exhibiting superior performance owning to the NO₃^? anion substitution for the OH^? in nickel hydroxide to form Ni₃(NO₃)₂(OH)₄, together with its interface synergy with ceria. In alkaline solution, the NNO/CeO₂/NF electrocatalyst could catalyze the OER with an overpotential of 330 mV to approach 50 mA cm^?2. Also, it needs only an overpotential of 120 mV to reach 10 mA cm^?2 for HER. Additionally, when a standard two-electrode water electrolyzer is fabricated by employing NNO/CeO₂/NF as both the cathode and anode, it can generate 10 mA cm^?2 at 1.64 V and operate steadily without performance degradation after 25 h. This research provides a novel perspective for reasonable design of advanced catalytic materials with improvements in the field of electrocatalysis.     

Mo-doped cobalt hydroxide nanosheets coupled with cobalt phosphide nanoarrays as bifunctional catalyst for efficient and high-stability overall water splitting

Exploring earth-abundant bifunctional electrocatalysts with highly efficient activity for overall water splitting is exceedingly challenging. Herein, a facile electrodeposit-phosphating-electrodeposit strategy is developed to obtain Mo-doped Co(OH)₂ nanofilms coupled with CoP nanosheets loaded on nickel foam (denoted as MoCo(OH)₂/CoP/NF). Benefitting from the unique structural merits, MoCo(OH)₂/CoP/NF exhibits outstanding electrocatalytic performance both for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). The results indicate that the dopant of Mo in the Co(OH)₂ can further improve the electrocatalytic performance. To achieve a current density of 10 mA cm^?2, only 15 and 287 mV are required for HER and OER in 1 M KOH solution, respectively. When MoCo(OH)₂/CoP/NF simultaneously employed as cathode and anode for overall water splitting, it only requires 1.593 and 1.853 V to achieve 10 and 50 mA cm^?2, respectively. The electrocatalytic activity of MoCo(OH)₂/CoP/NF for overall water splitting even exceed the benchmark electrode couple of Pt/C/NF||RuO₂/NF, and MoCo(OH)₂/CoP/NF perform excellent durability for overall water splitting. This work opens up new avenues for large-scale commercial production of overall water splitting catalysts due to its low-cost and facile method.     

Dysprosium doped copper oxide (Cu1-xDyxO) nanoparticles enabled bifunctional electrode for overall water splitting

The production of hydrogen, a favourable alternative to an unsustainable fossil fuel remains as a significant hurdle with the pertaining challenge in the design of proficient, highly productive and sustainable electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). Herein, the dysprosium (Dy) doped copper oxide (Cu_1-xDy_xO) nanoparticles were synthesized via solution combustion technique and utilized as a non-noble metal based bi-functional electrocatalyst for overall water splitting. Due to the improved surface to volume ratio and conductivity, the optimized Cu_1-xDy_xO (x = 0.01, 0.02) electrocatalysts exhibited impressive HER and OER performance respectively in 1 M KOH delivering a current density of 10 mAcm^?2 at a potential of ?0.18 V vs RHE for HER and 1.53 V vs RHE for OER. Moreover, the Dy doped CuO electrocatalyst used as a bi-functional catalyst for overall water splitting achieved a potential of 1.56 V at a current density 10 mAcm^?2 and relatively high current density of 66 mAcm^?2 at a peak potential of 2 V. A long term stability of 24 h was achieved for a cell voltage of 2.2 V at a constant current density of 30 mAcm^?2 with only 10% of the initial current loss. This showcases the accumulative opportunity of dysprosium as a dopant in CuO nanoparticles for fabricating a highly effective and low-cost bi-functional electrocatalyst 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.     

Facile synthesis of three-dimensional spherical Ni(OH)2/NiCo2O4 heterojunctions as efficient bifunctional electrocatalysts for water splitting

Synthesis of highly efficient, non-noble and bi-functional electrocatalysts is exceedingly challenging and necessary for water splitting devices. In this work, three-dimensional spherical Ni(OH)₂/NiCo₂O₄ heterojunctions are prepared by a one-step hydrothermal method and the hybrids are explored as efficient electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) in an alkaline electrolyte via tuning different Ni/Co atomic ratios of heterojunctions. The optimized Ni(OH)₂/NiCo₂O₄ (S (1:1)) exhibits high electrocatalytic activity with an ultralow over-potential of 189 mV at 10 mA cm⁻² for the HER. With regard to the OER, the over-potential of the as-synthesized S (1:1) heterojunction is only 224 mV at the current density of 10 mA cm⁻². The improved catalytic performance of the Ni(OH)₂/NiCo₂O₄ heterojunctions is attributed to the chemical synergic combining of Ni(OH)₂ and NiCo₂O₄, large specific surface area for exposing more accessible active sites, and heterointerface for activating the intermediates that facilitates electron/electrolyte transport. The prepared catalyst exhibits good durability and stability in HER and OER catalyzing conditions. This study provides a feasible approach for the building of highly efficient bifunctional water splitting electrocatalysts and stimulates the development of renewable energy conversion and storage devices.     

Oxygen plasma induced interfacial CoOx/Phthalocyanine Cobalt as bifunctional electrocatalyst towards oxygen-involving reactions

Performance of electrocatalysts towards oxygen-involving reactions is strongly associated with the surface and interface properties. Cobalt phthalocyanine (CoPc) materials have been widely explored as oxygen-involving electrocatalysts but their intrinsic catalytic activity is always poor. We present here a surface oxygen plasma approach to directly treat CoPc for producing interfacial CoO_x nanodots anchored on CoPc (CoO_x/CoPc), which exhibits high activity towards both oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). The optimized CoO_x/CoPc demonstrates a much better catalytic activity with a half-wave potential of 0.63 V and an average electron transfer number of 3.64 than the CoPc (0.59 V and n = 2.37) towards ORR in alkaline media. Moreover, OER performance of the CoO_x/CoPc is also significantly enhanced, showing a current density of 22.2 mA cm^?2 that is 36 times higher than that of CoPc (0.6 mA cm^?2) at an overpotential of 0.49 V. It is found that the enhanced performance of the CoO_x/CoPc is attributed to the high electrochemical active surface area, highly active CoO_x, as well as desired interfacial structure.     

Crossed FeCo2S4 nanosheet arrays grown on 3D nickel foam as high-efficient electrocatalyst for overall water splitting

Great efforts in developing low-cost, highly efficient and stable electrocatalysts are to tune the chemical compositions and morphological characteristics for enhancing efficiency of water splitting. In this communication, FeCo₂S₄ nanosheet was grown in situ on nickel foam (FeCo₂S₄/NF) via a facile hydrothermal sulfidization method and served as a high-efficient bifunctional electrocatalyst for overall water splitting. As-synthesized FeCo₂S₄/NF self-supported electrode delivers 20 mA cm^?2 at an overpotential of 259 mV toward OER and 10 mA cm^?2 at an overpotential of 131 mV toward HER in alkaline media. Moreover, when used as both anode and cathode in a two-electrode electrolyzer, only a small cell voltage of 1.541 V is needed to afford a current density of 10 mA cm^?2 for overall water splitting. Bifunctional electrode FeCo₂S₄/NF also revealed a distinguished electrochemical durability during a 12 h stability test at 1.63 V, which would provide a promising water splitting installation for commercial hydrogen production.