Modulation of crystal water in cobalt phosphate for promoted water oxidation

Abstract

Cobalt phosphate tetrahydrate was identified as the optimal Co-Pi phase for electrocatalytic oxygen evolution reaction.

Rapid and Scalable Synthesis of Prussian Blue Analogue Nanocubes for Electrocatalytic Water Oxidation†

“…For instance, at an applied potential of 1.8 V vs. RHE, CoCo‐PBA delivers a large normalized current density ( j Cdl @1.8V vs. RHE) of 1301.6 A·F –1 , while much smaller values of 297.2, 231.2 and 137.1 A·F –1 (equivalently, 4.38‐, 5.63‐ and 9.49‐folds enhancement) were resulted for CoFe PBA, FeFe PB and NiFe PBA (Table 1), respectively, confirming the excellent intrinsic OER activity of the CoCo‐PBA nanocubes. Of note, this value is also much larger than previous reports on Co‐based catalysts including porous α ‐Co(OH) 2 /Mo 9 O 26 hybrid nanosheets, [ 67 ] anhydrous and hydrated cobalt phosphates, [ 66 ] ternary NiCoFe oxide nanomesh, [ 43 ] NiCoFe spinel oxide/Fe wire [ 70 ] and the La 1– x Fe x CoO 3 nanocrystals, [ 40 ] indicating the superior OER activity of the CoCo‐PBA catalyst.…”

“…That is, the dominant peaks at 782.1 and 797.6 eV can be indexed as the Co 2+ ions, and the peaks located at 781.7 and 796.8 eV can be assigned to the Co 3+ species. [ 66‐67 ] In addition, the quantitative analysis from the integral peak area indicates that the Co 3+ /Co 2+ ratio in CoCo PBA is 0.11. Besides, C and N from the cyano group in the PBA lattice can be identified.…”

“…[ 72 ] Interestingly, a weak peak at 535.5 eV originated from the surface peroxide species can be identified for the catalysts after stability tests, which is consistent with previous reports on Co‐based OER catalysts after long‐term operation. [ 40,66 ] Overall, the pre‐oxidation process plays an important role in facilitating the OER catalysis, and the small particle size, facile charge transfer behavior and favorable Co 2+ ‐to‐Co 3+ conversion of the CoCo PBA pre‐catalyst could lead to remarkable accumulation of the catalytically active species. As a result, superior OER activity with dramatic performance improvement towards long‐term operation can be achieved for the CoCo PBA nanocubes, which provides promising catalysts for practical water electrolysis.…”

Recent advances in the pre-oxidation process in electrocatalytic urea oxidation reactions

“…by the transition metal-based catalysts, the electro-oxidation of urea also takes place on the metal sites in high valence, and the enrichment of the catalytically active high-valence metal sites is of great importance in accelerating the UOR process. [34][35][36]39,[49][50][51][52][53][54][55][56][57] Taking nickel hydroxide as an example, the UOR process can be divided into two basic steps, namely, an electrochemical pre-oxidation process of Ni(OH) 2 which leads to surface reconstruction and in situ generation of catalytically active highvalence Ni species (eqn (6); denoted as NiOOH for simplification) and a subsequent chemical oxidation of urea molecules on the asformed catalytically active Ni sites in high valence (eqn ( 7)): [43][44][45][46][47][48] 6Ni(OH…”

Molten-Salt-Protected Pyrolytic Approach for Fabricating Borate-Modified Cobalt–Iron Spinel Oxide with Robust Oxygen-Evolving Performance

“…Besides, the enrichment of Fe 3+ ions in CFO-B-MS can also be confirmed from the quantitative XPS analyses (Table S2). The higher binding energy of the metal sites and the enriched high-valence metal ions are beneficial to the electro-oxidation behavior, which may result in higher intrinsic activity toward OER catalysis. , In addition, the O 1s spectra shown in Figure C can be deconvoluted into two independent signals, where the peak at 520.1 eV can be assigned to the oxygen ions bonded with metal sites in the lattice, and the peak at 531.9 eV can be attributed to the oxygen vacancies. ,, As can be seen, more oxygen vacancies can be formed on the surface of CFO-B-MS, which could act as the active sites for OER. , Besides, Figure D depicts the B 1s spectra of CFO-B-MS and CFO-B, where the peaks located at 191.5–191.8 eV can be indexed as the B 3+ ions bonded with oxygen in the borate species, confirming the borate modification on the surface of the products. , …”