Pith. sign in

REVIEW 4 major objections 6 minor 3 references

Structure-Property Correlation of Cr/Cu-MnFeCoNi High-Entropy Alloys for Alkaline Water Electrolysis

T0 review · 4 major / 6 minor · reviewed 2026-07-30 · grok-4.5

Challenge this review Re-run · record.json Download PDF Read on arXiv ↗ Review JSON

Pith's one-line read Replacing chromium with copper in a MnFeCoNi high-entropy alloy improves both alkaline hydrogen and oxygen evolution.

desk verdict Solid Cr-vs-Cu head-to-head with a real OER reconstruction observation; the bifunctional ranking is credible, but the DFT story only cleanly supports HER. read the letter →

arxiv 2607.26888 v1 pith:VNBKP6PE submitted 2026-07-29 cond-mat.mtrl-sci

Shreyasi Chattopadhyaya , Raphael B. de Oliveira , Deepti Gangwar , Tymofii S Pieshkov , Marcelo L. Pereira Junior , Dhiman Banik , Astrid Campos-Mata , Atin Pramanik
show 5 more authors
Soumyabrata Roy Douglas S. Galvão Chandra Sekhar Tiwary Krishanu Biswas Pulickel M Ajayana
This is my paper · ORCID
classification cond-mat.mtrl-sci
keywords high-entropyalloysalkalinewaterelectrolysishydrogenevolutionreactionoxygenCrMnFeCoNiCusingle-elementsubstitutionsurfacereconstruction
verification ladder T0 review T1 audit T2 compute T3 formal

The pith

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The reading

This paper asks whether swapping one metal in a five-element high-entropy alloy is enough to change how well it splits water in base. The authors compare CrMnFeCoNi with MnFeCoNiCu under the same alkaline conditions and find that the copper version needs less extra voltage and runs with faster kinetics for both hydrogen and oxygen evolution. Calculations show copper softens how tightly the surface holds the key reaction intermediates, which matches the better experimental rates. After long oxygen-evolution testing the copper atoms migrate outward into a copper-rich shell, while hydrogen-evolution conditions keep the metals mixed. The practical point is that a single, cheap elemental swap can be used as a design knob for noble-metal-free water-splitting catalysts.

What carries the argument

Single-element Cr-to-Cu substitution inside an equiatomic FCC MnFeCoNi high-entropy alloy: copper acts as an electron acceptor that weakens intermediate binding relative to chromium-rich sites and, under OER, drives surface reconstruction into a Cu-rich outer shell.

What would settle it

Measure HER and OER overpotentials and post-test elemental maps on a series of MnFeCoNi–(Cr/Cu) alloys with systematically varied Cu fraction; if activity does not track the calculated intermediate binding strengths, or if a Cu-rich shell appears without the predicted activity change, the central claim fails.

Watch

Extended reading notes

Core claim

Under identical alkaline conditions, substituting Cr with Cu in the MnFeCoNi framework produces a bifunctional high-entropy alloy that outperforms the chromium analog for both HER and OER, reaching a lower HER overpotential of 538 mV and a Tafel slope of 165 mV dec⁻¹, because copper modulates the electronic structure to give more favorable binding energies for H*, O*, OH*, and OOH*.

Load-bearing premise

The binding energies calculated on a few stable bulk-like alloy surfaces are assumed to rank the real working catalysts even though oxygen evolution drives copper to the surface and forms a shell the models do not include.

Editorial extensions

If this is right

  • Compositional design of HEA water-splitting catalysts can start with targeted single-element swaps rather than full five-metal redesigns.
  • Cu-containing MnFeCoNi HEAs become candidates for low-cost bifunctional alkaline electrolyzer electrodes, with OER performance approaching RuO2 when carbon is added to the ink.
  • Post-OER Cu surface enrichment must be treated as part of the active catalyst state, not merely degradation.
  • HER stability benefits from the homogeneous multimetallic surface that persists under reducing conditions.

Reading between the lines

Editorial extensions of the paper, not claims the author makes directly.

  • If Cu shell formation is the main OER deactivation path, a thin protective overlayer or pulsed reverse bias might lock copper in place and extend lifetime.
  • The same Cr-to-Cu lever may transfer to other Cantor-derived HEAs used for CO2 reduction or nitrogen reduction where intermediate binding also limits rate.
  • Operando spectroscopy that tracks Cu oxidation state during the first few hundred OER cycles would test whether the calculated bulk-like sites ever exist under working conditions.
Share X Bluesky LinkedIn Reddit HN

Signed reviews

No signed human review yet.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, and a circularity audit.

Referee Report

4 major / 6 minor

Summary. The manuscript compares equiatomic CrMnFeCoNi (HEA-Cr) and MnFeCoNiCu (HEA-Cu) nanoparticles for alkaline HER and OER under matched conditions. XRD, XPS, SEM, and TEM/EDS establish single-phase FCC solid solutions with homogeneous elemental distributions as synthesized. Electrochemically, HEA-Cu outperforms HEA-Cr and pure Cu: HER onset/overpotential near 538 mV with Tafel slope 165 mV dec⁻¹ versus higher values for HEA-Cr, with analogous OER improvement; ADT, EIS, and post-test TEM show HER retains elemental homogeneity while OER drives Cu migration into a Cu-rich outer shell over a multimetallic core. DFT on selected FCC supercells with Monte Carlo adsorption sites reports weaker binding of H*, O*, OH*, and OOH* on HEA-Cu than HEA-Cr, offered as the electronic-structure rationale for the activity ranking and for single-element substitution as a bifunctional design rule.

Significance. If the Cr→Cu ranking and the reconstruction observation hold, the work is a useful, concrete case study of how one-element substitution in a Cantor-related MnFeCoNi framework tunes alkaline water-splitting kinetics and surface evolution. Strengths include matched synthesis/characterization of both alloys, carbon-free ink tests plus Vulcan-carbon comparisons, and especially the post-HER versus post-OER TEM/EDS contrast documenting Cu shell formation under OER. The HER performance (η ≈ 538 mV) is modest relative to state-of-the-art non-noble catalysts, so impact is primarily structure–property insight rather than a record bifunctional electrode. The DFT–experiment link is a genuine contribution only where the models represent the working surface; that link is stronger for HER than for OER given the reported reconstruction.

major comments (4)
  1. [Computational Analysis; Table 1; Figs. 5, 7–8] Computational Analysis / Table 1 / Figs. 7–8 vs Fig. 5: The load-bearing OER structure–property claim is that Cu substitution weakens binding of O*, OH*, and OOH* relative to Cr and thereby improves OER. Experiment, however, shows that after OER the working HEA-Cu surface is a Cu-rich outer shell over a multimetallic core (Fig. 5), not the homogeneous FCC termination used in DFT (one bulk-like structure per alloy; Monte Carlo sites on as-built supercells). Table 1 therefore ranks idealized as-synthesized surfaces, not the operando OER surface the paper documents. Either (i) compute intermediates on Cu-enriched / oxide–hydroxide shell models consistent with Fig. 5, or (ii) explicitly restrict the DFT OER claim to initial surfaces and separate the reconstruction discussion from the binding-energy design rule. Without one of these, the bifunctional electronic-structure explanation for OER i
  2. [§2.2 Electrochemical Characterization; Fig. 2; Abstract] §2.2 / Fig. 2c–d: Numerical OER overpotentials at 10 mA cm⁻² (and, preferably, at a higher current density) for HEA-Cr, HEA-Cu, and Cu are not stated in the text with the same clarity as the HER 538 mV value. The abstract and conclusion assert bifunctional superiority and a single 538 mV figure that reads as HER-only; OER claims need explicit η and Tafel numbers in the main text for both alloys under identical loading so the Cr→Cu improvement can be evaluated quantitatively, not only from unlabeled LSV curves.
  3. [§2.2; Fig. 2e–f] §2.2 / Fig. 2e–f: ECSA/C_dl is reported only for HEA-Cu (0.12 mF cm⁻², 3 cm²). Geometric j at fixed mass loading is used as the primary metric for HEA-Cr versus HEA-Cu (axiom implicit in the comparison). Without C_dl/ECSA (or another surface-normalization) for HEA-Cr under the same protocol, it is unclear whether the activity gain is intrinsic or partly area/roughness. Report ECSA for both alloys and, if feasible, ECSA-normalized LSV or specific activity at a fixed overpotential.
  4. [Abstract; Conclusion; Fig. 6] Language of “high-performance” / “efficient water electrolysis” (Abstract, Conclusion) sits uneasily with HER η₁₀ ≈ 538 mV and Tafel slopes of 165–226 mV dec⁻¹, which indicate sluggish Volmer–Heyrovsky kinetics relative to competitive alkaline HER HEAs and to Pt/C in Fig. 6. The Cr→Cu ranking can stand; the performance framing should be tempered to “improved relative to HEA-Cr under these conditions,” with clearer benchmarking against recent non-noble HEA HER/OER literature beyond RuO₂/Pt/C.
minor comments (6)
  1. [Figure 3 caption] Fig. 3 caption: panels (c, d) are labeled “LSV and EIS for HER” but the text discusses OER; correct to OER.
  2. [§2.1; Fig. 1c] XPS narrative inconsistency: early text states Cu is predominantly Cu(I) with mixed-valence discussion later (“Fe, Co and Cu exhibit mixed-valence”); align assignments and satellite interpretation for Cu 2p / Cu LMM.
  3. [§2.1–2.2; Abstract] Typographical/notation issues: “mVdec ¹” / missing superscripts; “cylces”; “Co–Cr–Fe–Mn–Ni” vs composition order; Ni 2p peak at 886.2 eV is unusually high and should be checked against fit/raw data.
  4. [§3 Computational Analysis] Computational methods (main text): state functional, code, supercell size, spin treatment, how ΔG_H / ΔG_O/OH/OOH and the U = −0.80 V, pH = 14 corrections are defined (Eq. references), and why only the third-most-stable HER structures and a single OER structure per alloy are emphasized. Point readers clearly to SI methodology.
  5. [Fig. 2a; Abstract; §2.2] Fig. 2a: clarify whether 0.538 V is onset or η at 10 mA cm⁻²; abstract says overpotential 538 mV while body mixes “onset potential” wording for the same numbers.
  6. [§2.2; Supporting Information] Report replicate statistics (error bars on η and Tafel) and iR-correction / RHE calibration protocol briefly in the main electrochemical section or SI cross-reference.

Circularity Check

0 steps flagged · score 0.0 of 10

No significant circularity: experimental ranking is independent of DFT; computation corroborates rather than defines the result.

full rationale

The load-bearing claim—that HEA-Cu outperforms HEA-Cr for alkaline HER and OER after Cr→Cu substitution—is established by direct electrochemical measurement (LSV overpotentials, Tafel slopes, EIS, ADT, ECSA) under identical conditions, not by fitting or by definition from theory. DFT (Monte Carlo adsorption on the most stable FCC supercells; ΔGH, ΔGO, ΔGOH, ΔGOOH) is run independently and then compared to the experimental ordering via standard Sabatier reasoning; the computed weaker binding on HEA-Cu is not fitted to the measured overpotentials and does not force them. Post-OER Cu-shell reconstruction is reported as an experimental observation and is not used as an input that tautologically produces the activity claim. Self-citations to related HEA/electrocatalysis work from overlapping groups supply background only and are not uniqueness theorems or load-bearing premises. Any mismatch between pristine-FCC DFT models and the operando Cu-rich OER shell is a correctness/representativeness concern, not circularity. Derivation chain is self-contained against external benchmarks.

Assumptions & free parameters 5 free parameters · 5 assumptions · 0 invented entities

The central claim rests on standard electrocatalysis and materials assumptions plus computational modeling choices, not on new physical entities. Free parameters are mainly experimental knobs (loading, cycle count) and DFT selection/ truncation choices that can affect quantitative ΔG but are not fitted to force the HEA-Cu > HEA-Cr ranking. No invented particles or forces.

free parameters (5)
  • Catalyst mass loading on GCE = 0.5 mg cm⁻²
    Optimized and fixed at 0.5 mg cm⁻² for ‘best’ homogeneous ink; changes geometric current density and apparent overpotential comparisons.
  • Number of ADT cycles = 3000
    Stability judged after 3000 cycles; choice affects observed activation (HER) versus mild decay (OER) narrative.
  • DFT structure subset for catalysis = top 5 of 100 (HER); 1 of those (OER)
    From 100 optimized cells per alloy, only the five most stable (HER) or one (OER) are used for adsorption energetics; ranking of alloys could depend on this truncation.
  • HER computational bias potential U = U = −0.80 V
    ΔG_H evaluated at fixed U = −0.80 V, pH 14, T = 300 K; absolute free energies shift with U though relative alloy ordering may be more robust.
  • Vulcan carbon fraction in comparative inks = 10 wt%
    10 wt% carbon added for ‘practical’ comparison to Pt/C and RuO₂; alters conductivity and apparent activity versus carbon-free primary data.
assumptions (5)
  • domain assumption Alkaline HER follows a Volmer–Heyrovsky pathway when Tafel slopes are in the ~160–230 mV dec⁻¹ range reported.
    Used to interpret Tafel slopes for Cu, HEA-Cr, and HEA-Cu in §2.2 without microkinetic fitting.
  • domain assumption Sabatier principle: intermediate binding should be neither too strong nor too weak; less negative ΔG near optimum implies faster HER/OER kinetics.
    Explicitly invoked in Computational Analysis to translate weaker HEA-Cu binding into higher activity.
  • domain assumption Standard DFT total-energy differences plus fixed electrochemical free-energy corrections suffice to rank HEA surface binding of H*, O*, OH*, OOH*.
    Underpins Table 1 and ΔG_H comparisons; functional, solvation, and coverage effects are not varied in the main text.
  • domain assumption Equiatomic arc-melted and cryo-milled powders form representative bulk FCC solid-solution surfaces for catalysis comparison.
    Structural claims in §2.1 (XRD single-phase FCC, TEM mapping) are taken as the active catalyst identity before reconstruction.
  • ad hoc to paper Geometric current density at fixed mass loading is a fair primary activity metric when comparing HEA-Cr and HEA-Cu.
    ECSA is reported only for HEA-Cu; intrinsic activity normalization between the two alloys is not established.

how reviews work

0 comments
Cite this review

Pith. "Pith review of Structure-Property Correlation of Cr/Cu-MnFeCoNi High-Entropy Alloys for Alkaline Water Electrolysis." pith.science (2026). https://pith.science/paper/VNBKP6PE

@misc{pith2026260726888,
  author       = {Pith},
  title        = {Pith review of: Structure-Property Correlation of Cr/Cu-MnFeCoNi High-Entropy Alloys for Alkaline Water Electrolysis},
  year         = {2026},
  howpublished = {\url{https://pith.science/paper/VNBKP6PE}},
  note         = {Machine review of arXiv:2607.26888}
}
read the original abstract

High-entropy alloys (HEAs), with their unique compositional-complexity and tunable surface chemistry, have emerged as promising electrocatalysts for energy conversion. The catalytic activity of HEA often arises from the interplay between the intrinsic activity of the individual elements and the synergistic effects generated at the interfaces. Even a single-element substitution in a multicomponent HEA can substantially alter the surface-chemistry and electrochemical kinetics of the active surface. Here we investigated the structure-property relationship of CrMnFeCoNi (HEA-Cr) and MnFeCoNiCu (HEA-Cu) HEAs by comparing the alkaline hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activity. Under the same experimental condition, HEA-Cu outperforms HEA-Cr towards both HER and OER. Substituting Cr with Cu significantly enhances the bifunctional activity, where HEA-Cu achieved a lower overpotential (538 mV) and Tafel slope (165 mVdec-1) when compared with HEA-Cr. Computational analysis corroborates these findings, showing that Cu substitution modulates the electronic-structure to provide favorable binding energies for reaction intermediates (H*, O*, OH*, and OOH*). Interestingly, unlike HER, recovered HEA-Cu after OER showed migration of Cu forming a Cu-rich outer layer shell with a multimetallic core. These findings demonstrate the potential of single-element substitution in HEAs as a strategy for designing high-performance, cost-effective catalysts for efficient water electrolysis.

Figures

Figures reproduced from arXiv: 2607.26888 by the authors.

Figure 1
Figure 1. Characterization of MnFeCoNiCu: (a) XRD; (b-g) XPS; (h-i) TEM analysis (j-o) TEM elemental mapping. characteristic of Mn4+ species, indicating that manganese predominantly exists in the +4 oxidation state within the alloy nanoparticles. Overall, the XPS analysis reveals that Cu, Ni, and Mn are present predominantly in single oxidation states, namely Cu , Ni ⁺ 2+, and Mn4+, respectively. In contrast, Fe and Co exhibi… view at source ↗
Figure 2
Figure 2. HER activity of MnFeCoNiCu HEA in 1M KOH: (a, b) LSV curves and Tafel plot of HEAs and Cu for HER, respectively; (c, d) LSV and Tafel plot of HEAs and Cu for OER, respectively. (e, f) ECSA measurement: (e) CV plot at different scan rate and (f) current density vs scan rate plot. (e) (f) (c) (d) (b) (a) [PITH_FULL_IMAGE:figures/full_fig_p009_2.png] view at source ↗
Figure 3
Figure 3. Stability analysis of MnFeCoNiCu by accelerated durability test for 3000 cycles. (a, b) LSV and EIS for HER; (c, d) LSV and EIS for HER. Electrochemical Impedance Spectroscopy was carried out to determine the charge-transfer resistance (RCT) values for the HEA, both before and after 3000 cycles. Figure 3b shows the Nyquist plots, where the x- and y-axes represent the real and negative imaginary parts of impedance, r… view at source ↗
Figures from the paper (5 more)
Figure 4
Figure 4. Figure 4: TEM analysis of the recovered HEA-Cu catalysts after HER. (a) TEM images, (b) HRTEM, (c-f) TEM-EDS mapping showing the distribution of the elements. formation of an outer layer (Figure 5c-k) was found for the catalyst recovered after OER, forming a near core-shell stru…
Figure 5
Figure 5. Figure 5: TEM analysis of the recovered HEA-Cu catalyst after OER. (a) TEM images, (b) HRTEM, (c-h) low-magnification TEM-EDS mapping (i-k) EDS mapping of magnified area close to the outer shell showing the distribution of the elements, (l) TEM image of the corresponding outer l…
Figure 6
Figure 6. Figure 6: HER and OER activity of HEA-Cu, HEA-Cr ink prepared with mixing 10% Vulcan C in 1M KOH: (a, b) LSV curves and overpotential of HEAs, respectively for HER; (c, d) LSV and overpotential of HEAs OER, respectively. Comparisons with RuO2 for OER and Pt/C for HER are also in…
Figure 7
Figure 7. Figure 7: (a) FeNiMnCoCu and (b) to FeNiMnCoCr, with the H atom placed at the most favorable adsorption site; (c) Gibbs Free Energy for each one of the structures. Atomic species are represented as Fe (yellow), H (red), Cu (purple), Mn (green), Co (mauve), Ni (silver), and Cr (o…
Figure 8
Figure 8. Figure 8: FeNiMnCoCu (a), (b), and (c), and FeNiMnCoCr (d), (e), and (f) structures selected from the OER analysis, with the O, OH, and OOH intermediate, respectively, placed at the most favorable adsorption site. Atomic species are represented as Fe (yellow), H (red), Cu (purpl…

Discussion (0). Continue with ORCID to comment.

Reference graph

Works this paper leans on

3 extracted references · 2 canonical work pages

  1. [1]

    Non-Noble Metal Catalysts for the Alkaline Hydrogen Evolution Reaction: A Review

    (1) Lawan, B. Non-Noble Metal Catalysts for the Alkaline Hydrogen Evolution Reaction: A Review. Discov. Chem. 2026 31 2026, 3 (1), 166-. https://doi.org/10.1007/S44371-026- 00555-2. (2) Chattopadhyay, S.; de Oliveira, C. C.; Bhar, R.; Banik, D.; Pieshkov, T. S.; Puthirath, A. B.; Pramanik, A.; Sreeram, P. R.; Saju, S. K.; Costin, G.; Vajtai, R.; Dubey, B....

    work page doi:10.1007/s44371-026- 2026

  2. [3]

    to Oganesson (Z = 118). J. Chem. Theory Comput. 2024, 20 (17), 7469–7478. https://doi.org/10.1021/ACS.JCTC.4C00784. (27) Bencherifa, I.; Belkhettab, I.; Derkaoui, K.; Dabou, O.; Chetoui, A.; Latreche, S.; Daoud, I. Unveiling the Impact of Al and Cr Alloying on Structure and HER Performance of CoCuZnMnNiFe High-Entropy Alloy Nanoparticles. J. Mater. Sci. 2...

    work page doi:10.1021/acs.jctc.4c00784 2024

  3. [429]

    (4) Medford, A

    https://doi.org/10.3390/CATAL11040429. (4) Medford, A. J.; Vojvodic, A.; Hummelshøj, J. S.; Voss, J.; Abild-Pedersen, F.; Studt, F.; Bligaard, T.; Nilsson, A.; Nørskov, J. K. From the Sabatier Principle to a Predictive Theory of Transition-Metal Heterogeneous Catalysis. J. Catal. 2015, 328, 36–42. https://doi.org/10.1016/J.JCAT.2014.12.033. (5) Wang, B.; ...

    arXiv 2015

Pith tools

Reviewed July 30, 2026 · model on record in the stance chip above.