Rational design of mixed-valence cobalt-based nanowires via simultaneous vanadium and iron modulations for enhanced alkaline electrochemical water splitting

Strategic modulation of the electronic structure and surface chemistry of electrocatalysts is crucial for achieving highly efficient and cost-effective bifunctional catalysts for water splitting. This study demonstrated the strategic incorporation of redox-active elements (vanadium (V) and iron (Fe)) to optimize the catalytic interface of mixed-valence cobalt-based nanowires (Co5.47N and CoP), which enhanced their hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalytic activity. Experimental and theoretical analyses revealed that the dual-cation doping increased the surface area and optimized the electronic structure of the nanowires, which promoted rapid water dissociation, favoured hydrogen adsorption kinetics, and stabilized the oxygen intermediates. Consequently, the V,Fe-Co5.47N and V,Fe-CoP nanowire electrocatalysts achieved low overpotentials of 55/251 and 63/265 mV for HER/OER at 10 mA cm-2 in 1 M KOH electrolyte, respectively, outperforming their pristine and single-cation-doped counterparts. The alkaline overall water-splitting devices assembled based on these bifunctional catalysts required an overall voltage of only 1.64 V and 1.66 V at 100 mA cm-2 and also demonstrated excellent durability. This work provides valuable insights into enhancing transition metal-based catalysts through the incorporation of redox-active elements for efficient water splitting.

Heterostructure Interface Engineering in CoP/FeP/CeOx with a Tailored d-Band Center for Promising Overall Water Splitting Electrocatalysis

Accomplishing a green hydrogen economy in reality through water spitting ultimately relies upon earth-abundant efficient electrocatalysts that can simultaneously accelerate the oxygen and hydrogen evolution reactions (OER and HER). The perspective of electronic structure modulation via interface engineering is of great significance to optimize electrocatalytic output but remains a tremendous challenge. Herein, an efficient tactic has been explored to prepare nanosheet-assembly tumbleweed-like CoFeCe-containing precursors with time-/energy-saving and easy-operating features. Subsequently, the final metal phosphide materials containing multiple interfaces, denoted CoP/FeP/CeO_x, have been synthesized via the phosphorization process. Through the optimization of the Co/Fe ratio and the content of the rare-earth Ce element, the electrocatalytic activity has been regulated. As a result, bifunctional Co3Fe/Ce0.025 reaches the top of the volcano for both OER and HER simultaneously, with the smallest overpotentials of 285 mV (OER) and 178 mV (HER) at 10 mA cm^-2 current density in an alkaline environment. Multicomponent heterostructure interface engineering would lead to more exposed active sites, feasible charge transport, and strong interfacial electronic interaction. More importantly, the appropriate Co/Fe ratio and Ce content can synergistically tailor the d-band center with a downshift to enhance the per-site intrinsic activity. This work would provide valuable insights to regulate the electronic structure of superior electrocatalysts toward water splitting by constructing rare-earth compounds containing multiple heterointerfaces.

Theoretical Study of Hydrogen Production from Ammonia Borane Catalyzed by Metal and Non-Metal Diatom-Doped Cobalt Phosphide

The decomposition of ammonia borane (NH3BH3) to produce hydrogen has developed a promising technology to alleviate the energy crisis. In this paper, metal and non-metal diatom-doped CoP as catalyst was applied to study hydrogen evolution from NH3BH3 by density functional theory (DFT) calculations. Herein, five catalysts were investigated in detail: pristine CoP, Ni- and N-doped CoP (CoPNi-N), Ga- and N-doped CoP (CoPGa-N), Ni- and S-doped CoP (CoPNi-S), and Zn- and S-doped CoP (CoPZn-S). Firstly, the stable adsorption structure and adsorption energy of NH3BH3 on each catalytic slab were obtained. Additionally, the charge density differences (CDD) between NH3BH3 and the five different catalysts were calculated, which revealed the interaction between the NH3BH3 and the catalytic slab. Then, four different reaction pathways were designed for the five catalysts to discuss the catalytic mechanism of hydrogen evolution. By calculating the activation energies of the control steps of the four reaction pathways, the optimal reaction pathways of each catalyst were found. For the five catalysts, the optimal reaction pathways and activation energies are different from each other. Compared with undoped CoP, it can be seen that CoPGa-N, CoPNi-S, and CoPZn-S can better contribute hydrogen evolution from NH3BH3. Finally, the band structures and density of states of the five catalysts were obtained, which manifests that CoPGa-N, CoPNi-S, and CoPZn-S have high-achieving catalytic activity and further verifies our conclusions. These results can provide theoretical references for the future study of highly active CoP catalytic materials.

Strategies for Developing Transition Metal Phosphides in Electrochemical Water Splitting

Electrochemical water splitting involving hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is a greatly promising technology to generate sustainable and renewable energy resources, which relies on the exploration regarding the design of electrocatalysts with high efficiency, high stability, and low cost. Transition metal phosphides (TMPs), as nonprecious metallic electrocatalysts, have been extensively investigated and proved to be high-efficient electrocatalysts in both HER and OER. In this minireview, a general overview of recent progress in developing high-performance TMP electrocatalysts for electrochemical water splitting has been presented. Design strategies including composition engineering by element doping, hybridization, and tuning the molar ratio, structure engineering by porous structures, nanoarray structures, and amorphous structures, and surface/interface engineering by tuning surface wetting states, facet control, and novel substrate are summarized. Key scientific problems and prospective research directions are also briefly discussed.

Facile synthesis of bimetallic-based CoMoO4/MoO2/CoP oxidized/phosphide nanorod arrays electroplated with FeOOH for efficient overall seawater splitting

CoMoO4/MoO2/CoP oxidized/phosphide nanorod arrays are fabricated for high performance in hydrogen evolution reaction, while the further electrodeposition of FeOOH results in excellent catalytic activity for the oxygen evolution reaction.

Phase-dependent electrocatalytic activity of colloidally synthesized WP and α-WP2 electrocatalysts for hydrogen evolution reaction

Transition metal phosphides (TMPs) have emerged as efficient non-noble electrocatalysts for hydrogen evolution reaction (HER).