Dual Doping of MoP with M(Mn,Fe) and S to Achieve High Hydrogen Evolution Reaction Activity in Both Acidic and Alkaline Media

Rational design of cost‐effective, high performance and stable hydrogen evolution reaction (HER) electrocatalysts in both acidic and alkaline media holds the key to the future hydrogen‐based economy. Herein, we introduce an effective approach of simultaneous non‐metal (S) and metal (Fe or Mn) doping of MoP to achieve excellent HER performance at different pH. The catalysts show remarkable overpotentials at −10 mA cm−2 of only 65 and 68 mV in 0.5 M H2SO4, and 50 and 51 mV in 1.0 M KOH, respectively, as well as much higher turnover frequencies compared to undoped MoP. Furthermore, the catalysts exhibit outstanding long‐term stability at a fixed current of −10 mA cm−2 for 40 h. The effects of both dopants, such as electronic structure modification and enhancement of the intrinsic activity, increase of the electrochemically active surface area, and formation of coordinatively unsaturated edge sites, act cooperatively to accelerate the HER at both pH media. Additionally, the presence of oxophilic Mn and Fe at the surface results in Mn or Fe oxide/hydroxide species that promote the dissociation of water molecules in alkaline electrolyte. This work introduces a facile and effective design principle that could pave the way towards engineering highly active HER catalysts for a wide pH range.Metal (Mn or Fe) and non‐metal (S) dual doped MoP catalysts were synthesiszed by reductive pyrolysis of the corresponding Mn,Mo‐ and Fe,Mo‐phosphonates precursors, in the presence of elemental S. The derived catalysts showed remarkable hydrogen evolution reaction (HER) activity in acidic and alkaline media. The dual doping process endowed MoP with proper hydrogen binding energy thus enhancing the HER in acidic media. In addition, Mn and Fe acted as surface oxides species in alkaline medium, which facilitated the water dissociation step. imageYousef Jameel Scholarship FundPeer Reviewe

Tuning the activity of cobalt 2-hydroxyphosphonoacetates-derived electrocatalysts for water splitting and oxygen reduction: insights into the local order by pair distribution function analysis

Pyrophosphate- or phosphide-based iron/cobalt electrocatalysts were prepared from the metal (R,S)−2-hydroxyphosphonoacetates to evaluate the effects of metal composition, N-doping and P-enrichment on the electrocatalytic activity. Rietveld and Pair Distribution Function analysis were used to determine phase composition. Irrespectively of the amorphous or crystalline nature, all pyrolyzed solids transformed under OER operation into biphasic Fe/CoO(OH), composed of discrete clusters (size ≤ 20 Å). Carbon paper-supported Fe0.2Co0.8O(OH) electrocatalysts displayed the best OER performances (overpotentials of 270–279 mV at 10 mA·cm−2), attributable to the formation of highly active bimetallic intermediate species. For HER, increased concentration of o-CoP in phosphide-based electrocatalysts resulted in improved performance, up to an overpotential of 140 mV. Employed as anode in alkaline water splitting, amorphous Fe-doped cobalt pyrophosphate and phosphide-derived electrocatalysts showed a cell voltage of 1.58 V at 10 mA·cm−2, with comparable stability to that of RuO2 and requiring lower voltage demand at high current densities.This work was funded by the PID2019-110249RB-I00/AEI/10.13039/501100011033; TED2021–129836B-I00/AEI/10.13039/501100011033/Unión Europea NextGenerationEU/PRTR (MICIU, Spain) and P20-00416 (Junta de Andalucia, Spain/FEDER) research projects. Synchrotron X-ray powder diffraction studies were performed at MSPD04 beamline at ALBA Synchrotron Light with the collaboration of ALBA staff. A.V.C. thanks MICIU for PRE2020-094459 student grant. R.M.P.C. acknowledges funding by project acknowledges B1_2022-23 (Plan Propio UMA). M.B.G. thanks PAIDI2020-DOC_00272 research grant (Junta de Andalucia, Spain). Funding for open access charge: Universidad de Málaga / CBUA

The Importance of Ligand Selection on the Formation of Bimetallic Phosphide Catalysts Derived from Metal-Organic Frameworks

Coordination polymers (CPs) and metal-organic frameworks (MOFs) have emerged as versatile precursors for transition-metal phosphides catalysts. However, the controlled synthesis of MOF-derived bimetallic phosphides remains a challenge, as mixtures of various phosphide phases are often formed. Here, it is shown that controlling the formation of pure CoMoP and CoMoP2 requires a careful choice of the ligands used to construct the MOF precursors, based on the chemical properties of the metals. In particular, the nature and number of the coordination moieties of the ligand play a key role. CoMoP and CoMoP2 particles coated with N-doped carbon were derived from phosphonate-based MOFs and compared as hydrogen evolution reaction (HER) electrocatalysts in acidic medium. CoMoP2 is more active and shows a turnover frequency (TOF) of 0.9 s-1 compared to 0.4 s-1 for CoMoP. The higher intrinsic activity of the CoMoP2 catalytic sites correlates with the differences in the electronic structure of the materials, with a larger charge transfer from the molybdenum to the phosphorous found for CoMoP2

High Electrocatalytic Performance of CuCoNi@CNTs Modified Glassy Carbon Electrode towards Methanol Oxidation in Alkaline Medium

A novel non-precious multiwalled carbon nanotubes (CNTs)—supported metal oxide electrocatalyst was developed for methanol electrooxidation in alkaline medium. The catalyst was fabricated by simultaneous electrodeposition of copper-cobalt-nickel ternary nanostructures (CuCoNi) on a glassy carbon electrode (GCE) modified with CNTs. The proposed electrode was characterized using X-ray diffraction (XRD), energy dispersive X-ray (EDX), and scanning electron microscopy (SEM). The electrochemical behavior and the electrocatalytic performance of the suggested electrode towards the oxidation of methanol were evaluated by cyclic voltammetry (CV), linear sweep voltammetry (LSV), and chronoamperometry (CA) in alkaline medium. Several parameters were investigated, e.g., deposition time, potential scan rate, etc. Compared to Cu, Co, or Ni mono electrocatalysts, the electrode based on ternary-metals exhibited superior electrocatalytic activity and stability towards methanol electrooxidation. For instance, CuCoNi@CNTs/GCE has shown at least 2.5 times electrocatalytic activity and stability compared to the mono eletrocatalysts. Moreover, the present study found that the optimized loading level is 1500 s of simultaneous electrodeposition. At this loading level, it was found that the relation between the Ip/ν1/2 function and scan rate gives the characteristic features of a catalytic process. The enhanced activity and stability of CuCoNi@CNTs/GCE was attributed to (i) a synergism between three metal oxides coexisting in the same structure; (ii) the presence of CNTs as a support for the metal oxides, that offers high surface area for the deposited tertiary alloy and suppresses the aggregation and sintering of the metals oxide with time; as well as (iii) the increase of the conductivity of the deposited semiconducting metal oxides

Operando Diffuse Reflectance UV-VIS Spectroelectrochemistry for Investigating Oxygen Evolution Electrocatalysts

This is a complete self-standing study on operando diffuse reflectance UV-vis spectroelectrochemistry for investigating oxygen evolution electrocatalysts.</div