Quantification of Hydride Coverage on Cu(111) by Electrochemical Mass Spectrometry

Abstract

Electrochemical mass spectrometry (EC-MS) is combined with chronoamperometry to quantify H coverage associated with the surface hydride phase on Cu(111) in 0.1 mol/L H2SO4. A two-step potential pulse program is used to examine anion desorption and hydride formation, and the inverse, by tracking the 2 atomic mass unit (amu) signal for H2 production in comparison to the charge passed. On the negative potential step, the reduction current is partitioned between anion desorption, hydride formation, and the hydrogen evolution reaction (HER). For modest overpotentials, variations in partial processes are evident as inflections in the chronoamperometry and EC-MS signal. On the return step to positive potentials, hydride decomposition by H recombination to H2 occurs in parallel with sulfate adsorption. The challenge associated with the inherent diffusional delay in the EC-MS response is mitigated by total H2 collection and steady-state analysis facilitated by the thin-layer EC-MS cell geometry as demonstrated for the HER on a non-hydride forming Ag electrode. Analysis of the respective transients and steady-state response on Cu(111) reveals a saturated hydride fractional coverage of 0.67 at negative potentials with an upper bound charge of 106 μC/cm2 (average electrosorption valency of ≈1.76) associated with adsorption of the (√3 × √7) mixed sulfate-water adlayer at positive potentials.

SHINERS Study of Chloride Order–Disorder Phase Transition and Solvation of Cu(100)

“…Several recent reports of hydride formation on Cu surfaces at more negative potentials motivate further exploration of the interplay between anion desorption, hydride formation, and the hydrogen evolution reaction. − ,,− Extending the negative vertex of the voltammetric scan below −1.25 V reveals a second much sharper current peak at −1.05 and −1.085 V in halide containing sulfuric and perchloric acid electrolytes (Figure and Figure S10, respectively). ,,,,, Comparison with SXRD studies in 1 mmol/L HCl + 0.1 mol/L HClO 4 reveals that the peak potential coincides with the disappearance of the c(2 × 2) superstructure (Figures and ). ,, The 40 mV difference in the peak potentials between the two supporting electrolytes indicates the modest impact of the oxyanion on the double-layer structure and halide adsorption dynamics. In halide-free perchloric acid media, ECSTM reveals the onset of hydride formation as a p(1 × 8) structure begins below −1.005 V SSE followed by densification to c­(p × 8) by –1.055 V. , The hydride phase forms in parallel with and catalyzes the hydrogen evolution reaction.…”

In Situ/Operando Methods for Understanding Electrocatalytic Nitrate Reduction Reaction

“…Electrochemical in situ DEMS measurements are commonly used for the detection of volatile intermediates/products. [136][137][138][139][140] Volatile samples are collected through a porous cylindrical tip (assembled near the surface of the electrode) and volatile intermediates/products are detected when the potential changes during cyclic voltammetry (CV) measurements. [69] Cu-modified Pt(100) electrodes were synthesized by Koper et al [141] The selective conversion from NO 3 − to N 2 can be achieved on Cu/Pt (100).…”

Synthesis, Structural Characterization, and CO2Reactivity of a Constitutionally Analogous Series of Tricopper Mono-, Di-, and Trihydrides

“…Increasing energy demand and continued reliance on fossil fuel-derived electricity couple to exacerbate anthropogenic climate change. − Atmospheric decarbonization through carbon dioxide (CO 2 ) capture and reduction (CO 2 RR) is a prominent strategy to curtail unsustainable greenhouse gas emissions. − Copper is a privileged catalyst for CO 2 RR, uniquely capable of producing hydrocarbon products. − Following the seminal work of Hori, − myriad studies, both experimental and computational, have investigated the properties of copper that facilitate this privileged ability to deoxygenate and couple CO x feedstocks. ,− Whereas the operative mechanism(s) remain ambiguous, surface copper hydrides are commonly invoked along the reduction pathway. ,,− Hydrogen adsorption dramatically alters the morphology and chemical properties of the reactive surface. − Indeed, hydride coverage is proposed to be the defining factor in dictating CO 2 RR versus competing proton reduction. , Surface hydrides are likewise crucial in the initial fundamental steps of CO 2 RR, controlling a mechanistic branching point for either the generation of formate complexes or CO 2 activation/metallocarboxylic acid formation en route to further reduced products (Figure A). , Structural changes due to surface hydrogenation remain ill-defined, given the challenges associated with studying bulk heterogeneous systems, yet they influence stability and activity in all aqueous copper electrocatalysis . Current molecular models lack fidelity, offering limited mechanistic insight.…”