Synthesis of lawn-like NiS2 nanowires on carbon fiber paper as bifunctional electrode for water splitting

a low-cost electrode with lawn-like NiS₂ nanowire arrays on flexible carbon fiber paper was synthesized, for the first time, via sulfurization of Ni₂(CO₃)(OH)₂ precursor. And the performance of this electrode as a bifunctional electrocatalyst toward both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) was evaluated. It shows that NiS₂ NWs/CFP requires small overpotentials of 165 mV for HER and 246 mV for OER, respectively, to deliver the current density of 10 mA cm^?2 in 1.0 M KOH. The corresponding symmetric two-electrode alkaline water electrolyzer only needs a cell voltage of 1.59 V to afford 10 mA cm^?2 water-splitting current density.     

Carbon supported bifunctional Rh–Ni(OH)2/C nanocomposite catalysts with high electrocatalytic efficiency for alkaline hydrogen evolution reaction

Pt group metals display lower HER activity in alkaline solution than in acidic solution, because they are inefficient in the water dissociation step (Volmer step). Compared with Pt, the activity difference of Rh in alkaline and acidic media is much smaller. Meanwhile, Ni(OH)₂ is proved to be an effective catalyst for water dissociation. Therefore, Rh–Ni(OH)₂/C nanocomposites with different Rh:Ni(OH)₂ ratios were synthesized by a co-deposition/partial reduction method, and their microstructures as well as electrocatalytic properties were studied. The results show that Rh and Ni(OH)₂ display synergistic effect in Rh–Ni(OH)₂/C nanocomposites. The Rh–Ni(OH)₂/C nanocomposite with a molar ratio of Rh to Ni(OH)₂ of 1:1 exhibits the highest activity. It shows an overpotential of 36 mV at 10 mA cm^?2 and a Tafel slope of 32 mV dec^?1 for HER in alkaline media, which is superior to commercial Pt/C. In addition, the Rh–Ni(OH)₂/C (1:1) nanocomposite shows excellent durability in alkaline media as well.     

Synthesis of non-noble NiMoO4–Ni(OH)2/NF bifunctional electrocatalyst and its application in water-urea electrolysis

Electrochemical water splitting to produce hydrogen is one of the most important technologies for energy storage and conversion. Urea oxidation reaction (UOR) with a lower electrode potential instead of oxygen evolution reaction (OER, water-splitting anode) in the water-urea electrolysis is an energy-saving approach. In this paper, NiMoO₄–Ni(OH)₂/NF is synthesized by hydrothermal reactions and explored as both hydrogen evolution reaction (HER) and UOR catalyst electrodes. This composite catalyst shows high catalytic bifunctional activities towards both HER and UOR. To validate both catalytic UOR and HER activities and durability, a two-electrode water-urea electrolyzer composed of NiMoO₄–Ni(OH)₂/NF as both anode and cathode materials is constructed (NiMoO₄–Ni(OH)₂/NF||NiMoO₄–Ni(OH)₂). Experiments show that a voltage of 1.341 V with a high stability (over 3000 CV cycles) can be achieved at 10 mA cm⁻², which are much better than those obtained using a Pt/C||IrO₂.     

Facile synthesis of cotton flower like Ni–Co/Ni–Co–O–P as bifunctional active material for alkaline overall water splitting and acetaminophen sensing

The development of electrode materials with simple preparation, favorable price, excellent electrocatalytic activity, and stability are some of the most important issues in the field of electrochemistry. Herein, we prepared Ni–Co/Ni–Co–O–P cotton flower like on a copper sheet (CS) by a convenient, efficient, and scalable electrodeposition method. The Ni–Co/Ni–Co–O–P was employed as effective binder free electrode material in two different applications such as electrocatalytic water splitting and acetaminophen (APAP) sensor. Remarkably, the Ni–Co/Ni–Co–O–P@CS exhibits low overpotentials of 310 and 90 mV at 10 mA cm^?2 for oxygen and hydrogen evolution reactions in alkaline media, respectively. Besides, the Ni–Co/Ni–Co–O–P@CS || Ni–Co/Ni–Co–O–P@CS couple needs a low cell voltage of 1.62 V to achieve a current density of 10 mA cm^?2, and its potential change is negligible after 20 h of continuous operation. Furthermore, Ni–Co/Ni–Co–O–P displays good electrochemical sensing performance toward APAP with a high sensitivity of 803.74 μA mM^?1cm^?2, low limit of detection of 0.16 μM, a wide linear range of 0.05 mM–3 mM, and a fast response time of 3.3 s. This work proposes a simple approach for synthesis of Ni–Co/Ni–Co–O–P as an efficient electrode material for water splitting and APAP sensing.     

In-situ “encapsulation” of Mo:Mo2C with nano-mosaic structure on wood-derived carbon for hydrogen evolution reaction

Coupling metallic and Mo₂C phases uniformly on conductive matrix at nanoscale is a promising route to solve the poor electrical conductivity and aggregation problems of nano-Mo₂C. In this work, a 3D self-supporting carbonized wood (CW) electrode encapsulation with mosaic structure Mo:Mo₂C for hydrogen evolution reaction was fabricated successfully by a facile annealing treatment and a gas-solid reaction. The presence of Mo phase accelerated the transfer rate of electrons and provided heterogeneous interface. The obtained electrode shows abundant catalytic active sites and low electrochemical impedance, thus improving the catalytic process of splitting water for HER. The Mo:Mo₂C-775 electrode requires an overpotential of 73.5 mV and 117 mV to achieve the current density of 10 mA cm^?2 in 0.5 M H₂SO₄ and 1.0 M KOH, respectively. Moreover, Mo:Mo₂C-775 electrode displayed excellent stability performance, which almost maintained a constant current density for 12 h (at ?100 mV vs RHE) in 0.5 M H₂SO₄ and 1.0 M KOH, respectively. This study provides a new idea for preparation of efficient 3D self-supporting electro-catalyst for HER.     

Orientated carbon nanotubes boosting faster charge transfer for bifunctional HER and OER

Orientated Carbon nanotubes would expose more active sites and have better electrical conductivity, while most of the carbon nanotubes are disordered, so it is necessary to align with the aid of external force. Hence, we obtain the stretchable films (denoted as PMC) by casting the solution of hydrothermal MWCNTs (ho-MWCNTs) and poly (vinyl alcohol) (PVA), following the Ni(OH)₂ deposited on PMC (denoted as PMC/Ni). XPS and XRD confirmed the charge transfer between ho-MWCNTs and PVA, which means generation of electronic delocalization center. Furthermore, the alignment of ho-MWCNTs could be observed by SEM. Meanwhile, PMC/Ni exhibited excellent catalytic performance for OER and HER in 1 M KOH. It only require 320 mV to achieve 20 mA cm^?2 for OER and a low overpotential of ?219 mV to achieve 10 mA cm^?2 for HER in 1 M KOH. The results verify that orientated ho-MWCNTs have a positive effect in promoting catalytic performance by promoting to faster electron transfer and more active sites. Hence, we believe that the catalytic performance of other hollow-tubes materials would show a strong relationship with the orientation, which needs more efforts to research.     

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.     

Study of cobalt boride-derived electrocatalysts for overall water splitting

The production of clean hydrogen fuel by the electrolysis of water requires highly active, low-cost and facilely prepared electrocatalyst that minimizes energy consumption. Here we report an active cobalt boride (CoB)-derived electrocatalyst for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). The CoB catalyst can be readily deposed on 3D nickel foam (NF) using a simple electroless plating method. A comprehensive analysis of the CoB catalyst with scanning electron microscopy transmission (SEM), transmission electron microscopy (TEM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) techniques revealed that CoOOH is formed on the surface of CoB catalyst during the OER process and Co(OH)₂ is formed in the HER process. The catalyst derived from CoB/NF exhibits low overpotentials towards both OER and HER in alkaline solution. The electrolysis cell using the CoB-derived catalyst couple requires a cell voltage of 1.69 V to afford a current density of 10 mA/cm², which compares favorably with most non-noble bifunctional electrocatalysts. The favorable combination of high-performance, low cost and facile preparation suggests that transition metal borides may act as promising electrocatalyst for water splitting.     

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.     

Nanoporous CoCu layered double hydroxide nanoplates as bifunctional electrocatalyst for high performance overall water splitting

The electrochemical water splitting into hydrogen and oxygen is the promising way for renewable hydrogen production as a carbon-neutral fuel, along with oxygen as a by-product. Herein, a novel nanoporous CoCu-layered double hydroxide (LDH) bifunctional electrocatalyst is fabricated by the hydrothermal method. The outstanding activity is mainly attributed to the incorporation of Cu²⁺ that promotes conductivity and enhances the electrochemical properties. As-prepared CoCu-LDH nanostructure works as efficient and stable water-splitting-electrolyzer and produces the voltage of 1.60 V at the current density of 10 mA cm^?2, which is better than catalyst based on the combination of commercial IrO₂ and Pt/C. Due to high electrocatalytic performance, together with its low cost and natural abundance of LDHs, it is expected that CoCu LDH can act as a candidate catalyst in the commercial alkaline overall water splitting.