Fe-Co coatings were electrodeposited on Cu substrates from a choline chloride-urea eutectic solution. The influence of Fe and Co content on the magnetic, morphological, and electrocatalytic properties of the electrodeposits was duly studied. The coercivity and quadrature of the magnetic hysteresis curves revealed that all coatings had soft magnetic properties that varied with the coating composition. A hyperfine magnetic field between 36 and 38 T in their Mössbauer spectra indicated the formation of Fe–Co alloy in the samples Fe87Co13, Fe64Co36, and Fe44Co56. All coatings with Fe content higher than 25% showed magnetic texture along their growth axis with orientation angles ranging from θ = 5.1 to 42.8∘. The Fe, Co, and Fe–Co coatings showed good electrocatalytic performance for the hydrogen evolution reaction, with mainly the Fe-rich coatings presenting the lowest values of overpotential. Remarkably, an Fe coating afforded a current density of 10 cm−1 at a low overpotential of 89.2 mV, as well as exhibiting a small Tafel slope of 44.6 mV dec−1 in 0.5 mol L−1 NaOH. The results showed that the use of choline chloride-urea eutectic solution provides a promising and ecological strategy for the production of Fe–Co coatings since it is not necessary to add other chemicals besides the corresponding metallic salts.

Agradecimentos: T.S. acknowledges vetenskaprådet (grant no. 2015-06462); X.Z. acknowledge Air Force Office of Scientific Research (AFOSR-Grant No. FA9550-14-1-0268), and C.F.W. thanks São Paulo Research Foundation (FAPESP-grant no. 2016/12340-9) for their financial support. Computational and financial support from the Center for Computational Engineering and Sciences at Unicamp through the FAPESP/CEPID grant no. 2013/08293-7, is acknowledged. EPMA facility at the Department of Earth Science, the Electron Microscopy Center (EMC), and shared equipment authority (SEA) at Rice University are acknowledged. Dr. Ashok Kumar and Hari Kishan are kindly acknowledged for their inputs

Abstract: A systematic investigation was conducted of the surface properties and the HER at electrodes of nominal composition Ti/RhxTi((1-x))O-y prepared by thermal decomposition (T-cal: 500 degrees C; t(cal): 2h; O-2 flux: 5 dm(-1) min(-1)) from salt precursor solutions dissolved in 6.0 mol dm(-3) HNO3. Films were characterized ex situ by SEM, EDX, XPS and XRD and in situ by open circuit potential measurements and CV. The electrochemical behaviour was investigated by CV as function of the anodic, E-lambda,E-a, and cathodic, E-lambda,E-c, switching potentials showing the Rh surface oxidation states strongly depend on these experimental variables. Surface Rh-sites are reduced to metallic rhodium in the cathodic potential region while higher oxidation states (I-III) are formed at more positive potentials (E >= 0.5 V/RHE). Hydrogen adsorption and desorption peaks as well as a short double layer charging region are observed at intermediate potential values. The HER was investigated by Tafel coefficients and reaction order with respect to H+ as function of nominal Rh-content

Hydrogen has been proposed to be a clean and carbon-neutral energy carrier that can be used as next generation fuel. Water splitting has long been thought to be a sustainable and environmentally friendly approach to hydrogen production, given that water is virtually an inexpensive, renewable, plenty resource and water splitting process itself does not produce any harmful emissions. The major challenge for the development of water electrolyzers for large scale production of hydrogen is huge energy consumption, originating from high overpotentials of the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). Transition metal phosphides have recently emerged as a new class of electrocatalysts that can efficiently catalyze the OER and HER. However, the catalytic performance needs to be further improved to promote the practical application of phosphide catalysts in the water splitting . In this work, two strategies are investigated to increase the hydrogen evolution reaction, oxygen evolution reaction as well as the overall water splitting performance of phosphide catalysts. The first strategy is to dope nickel atoms into cobalt-based phosphide catalyststo improve the intrinsic activity of each active site. The as-synthesized powdery phosphide catalysts showed narrow particle size distribution of 5-10 nm and good water splitting performance. Low overpotentials of 0.26 and 0.13 V could deliver a benchmark current density of 10 mA cm-2 in 1.0 M KOH for the oxygen and hydrogen evolution, respectively. Benefitting from the excellent OER and HER catalytic performance, a low cell voltage of 1.70 V was needed for the overall water splitting at 10 mA cm-2 , outperforming the performance of noble metal based catalysts under the same conditions. Meanwhile, the electrolyzer was able to operate at 10 mA cm-2 over 40 h with negligible degradation, showing good long-term stability. The second strategy is to prepare self-supported porous cobalt phosphide to increase the number of active sites on a given geometric surface area of electrodes. The as-prepared porous cobalt phosphide self-supported electrode showed outstanding water splitting performance, especially at high current densities. For instance, to afford overall water splitting at an industry-relevant current density of 1000 mA cm-2 , a low voltage of only 1.98 V was required. More importantly, the electrolyzer could sustain continuous electrolysis for 500 h at 500 mA cm-2 without obvious degradation.

We report the fabrication of p-type silicon (Si) photocathodes consisting of well-ordered Si microwire (Si-MW) arrays coupled with non-precious and earth-abundant amorphous oxygen-rich molybdenum oxysulfide (MoOxSy) as both a hydrogen evolution catalyst and a passivation layer. The MoOxSyis conformally grown on the Si-MW surface through photo-assisted cyclic voltammetric (CV) deposition. By adjusting the cycle numbers of the CV deposition, Si-MW array electrodes with different MoOxSy catalyst loadings (Si-MWs@MoOxSy) have been obtained and comprehensively characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X- ray photoelectron spectroscopy (XPS), and Raman and Fourier-transform infrared spectroscopies. The photoelectrochemical performance of the Si-MWs@MoOxSycathodes toward water reduction is investigated and compared with that of platinum nanoparticle decorated Si-MW array electrodes (Si-MWs@PtNPs). An optimized Si-MWs@MoOxSyphotocathode is found to exhibit activity compar- able to that of the Si-MWs@PtNPs one, with a much better stability in acidic medium. In neutral electrolyte, Si-MWs@MoOxSyoutperforms Si-MWs@PtNPs in terms of both activity and stability. Given the low materials cost, easy and well-established electrode fabrication procedure, and high demonstrated photoelectrochemical performance, the Si-MWs@MoOxSyarrays reported here hold substantial promise for use as low-cost and efficient photocathodes for water reduction.

Electrochemical water splitting powered by renewable energy (e.g. solar, wind) has been recognized as a sustainable and environmentally-friendly way to produce "green" hydrogen. Significant efforts were dedicated recently to developing cheap and efficient earth-abundant electrocatalysts to make electrolyzed hydrogen economically competitive. Notwithstanding substantial progress, the operational voltage of water splitting in a single electrolyte system is still high, even highly efficient electrocatalysts are used to catalyze the hydrogen evolution (HER) and oxygen evolution reactions (OER). Taking into account that the HER and the OER are kinetically favorable in electrolytes with different pH values, in this work we demonstrate that overall water splitting can be accomplished in acid-alkaline dual electrolytes with an onset voltage as low as 1.13 V, enabled by a bipolar membrane (BPM) under the "reverse bias" condition with the novel dual-phase cobalt phosphide-cobalt ditelluride (CoP-CoTe2) nanowires being used as efficient and durable bifunctional catalysts. Furthermore, we show that using a BPM under the "forward bias" the voltages needed to reach 10 and 100 mA cm(-2) can be reduced to 1.01 and 1.37 V, respectively, due to the assistance of electrochemical neutralization resulting from the crossover of electrolytes. The bipolar membrane water electrolysis (BPMWE) can be sustained for at least 100 h without notable degradation.

(Excerpt) Pt-based materials are the benchmarked catalysts in the cathodic hydrogen evolution reaction (HER) of water splitting; the prohibitive cost and scarcity of Pt immensely impede the commercialization of hydrogen energy. Ru has aroused significant concern because of its Pt-like activity and much lower price. However, it’s still a top priority to minimize the Ru loading and pursue the most superior cost performance. Herein, N-rich covalent organic framework (COF) was employed to assist the preparation of ultrafine Ru, including nanoclusters and single atoms loaded onto porous N-doped carbon by a simple impregnation-pyrolysis process with a low Ru content of 6.60 wt%, exhibiting superior HER activity with mass activity of 21.86 and 11.52 A mg-1 Ru (@100 mV) in alkaline and acidic conditions, separately 14.7 and 2.12 times higher than that of commercial Pt/C.