Hydrogen Spillover-Bridged Volmer/Tafel Processes Enabling Ampere-Level Current Density Alkaline Hydrogen Evolution Reaction under Low Overpotential

Abstract

Water-alkaline electrolysis holds a great promise for industry-scale hydrogen production but is hindered by the lack of enabling hydrogen evolution reaction electrocatalysts to operate at ampere-level current densities under low overpotentials. Here, we report the use of hydrogen spillover-bridged water dissociation/ hydrogen formation processes occurring at the synergistically hybridized Ni 3 S 2 /Cr 2 S 3 sites to incapacitate the inhibition effect of high-current-density-induced high hydrogen coverage at the water dissociation site and concurrently promote Volmer/Tafel processes. The mechanistic insights critically important to enable ampere-level current density operation are depicted from the experimental and theoretical studies. The Volmer process is drastically boosted by the strong H 2 O adsorption at Cr 5c sites of Cr 2 S 3 , the efficient H 2 O* dissociation via a heterolytic cleavage process (Cr 5c -H 2 O* + S 3c (#) → Cr 5c -OH* + S 3c -H # ) on the Cr 5c /S 3c sites in Cr 2 S 3 , and the rapid desorption of OH* from Cr 5c sites of Cr 2 S 3 via a new water-assisted desorption mechanism (Cr 5c -OH* + H 2 O(aq) → Cr 5c -H 2 O* + OH − (aq)), while the efficient Tafel process is achieved through hydrogen spillover to rapidly transfer H # from the synergistically located H-rich site (Cr 2 S 3 ) to the H-deficient site (Ni 3 S 2 ) with excellent hydrogen formation activity. As a result, the hybridized Ni 3 S 2 /Cr 2 S 3 electrocatalyst can readily achieve a current density of 3.5 A cm −2 under an overpotential of 251 ± 3 mV in 1.0 M KOH electrolyte. The concept exemplified in this work provides a useful means to address the shortfalls of amperelevel current-density-tolerant Hydrogen evolution reaction (HER) electrocatalysts.

Rhodium nanocrystals on porous graphdiyne for electrocatalytic hydrogen evolution from saline water

“…The free energies reflecting the adsorption ability OH* and H* species on the active sites were calculated. It was found that the adsorbed OH*species can be easily removed from the corner site to form an OH - anion (0.31 eV), which fits well with the widely accepted one-electron reductive desorption mechanism (OH* + e − → OH − ) 74 – 76 . While the generated hydrogen atoms (H*) are strongly bound to the corner sites with large free-energies of 0.82 and 0.86 eV for Heyrovsky step (H* + H 2 O + e − →H 2 * + OH − ) and Tafel step (2H* → H 2 *), respectively, which inhibit the formation of hydrogen molecule (H 2 ).…”

Ru@Ni3S2 nanorod arrays as highly efficient electrocatalysts for the alkaline hydrogen evolution reaction

“…Therefore, various Ni 3 S 2 -based heterostructures have been developed for the electrocatalytic hydrogen evolution reaction. 8,[28][29][30][31][32][33] Feng et al designed Cu nanodot-decorated Ni 3 S 2 nanotubes supported on carbon fibers as efficient electrocatalysts for the HER in alkaline media. The strong synergistic effect between Cu nanodots and Ni 3 S 2 nanotubes endows the hybrid electrocatalyst with excellent HER catalytic performance.…”

Boosting the interfacial hydrogen migration for efficient alkaline hydrogen evolution on Pt-based nanowires

“…2,10 In this case, the formed *H has to be transferred from the TM phase to the Pt phase in the rst place, followed by the hydrogen combination and desorption on Pt sites. [11][12][13] In this regard, hydrogen spillover is a recent focus that offers new insights to enhance the *H supply and HER activity of binary catalysts. 12,[14][15][16][17] Hydrogen spillover typically proceeds through hydrogen migration from H-enriched sites (strong *H adsorption sites) to H-decient sites (weak *H adsorption sites), similar to the case of the abovementioned binary system.…”

“…[11][12][13] In this regard, hydrogen spillover is a recent focus that offers new insights to enhance the *H supply and HER activity of binary catalysts. 12,[14][15][16][17] Hydrogen spillover typically proceeds through hydrogen migration from H-enriched sites (strong *H adsorption sites) to H-decient sites (weak *H adsorption sites), similar to the case of the abovementioned binary system. 15,18 Interestingly, due to the moderate DG H on Pt sites close to the thermoneutral point, Pt atoms can act as *H donating sites or accepting sites depending on the *H binding strength of the secondary component.…”

“…10,13,[19][20][21] Although hydrogen spillover was rst discovered in acidic HER systems, current research has also witnessed the spillover behavior in the alkaline HER, which is benecial to strengthening the *H supply for Pt-based binary catalysts in alkali. 10,12,22,23 It must be pointed out that because hydrogen spillover from strong to weak *H sites is intrinsically thermodynamically unfavorable, it will inevitably require an adequate driving force. 18 Moreover, the hydrogen spillover across the interfaces has to overcome the high migration kinetic barriers.…”