{"id":"1500d75a-fa0c-494b-961f-7fea1467298c","arxiv_id":"2502.05809","paper_version":2,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":7.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":3,"one_line_summary":"PEO smooths zinc electrodeposition by binding to the copper substrate and biasing nucleation toward flat-lying Zn(002) platelets, rather than by interacting with the growing zinc.","lead":"Using live atomic force microscopy, the authors show that polyethylene oxide (PEO) smooths zinc plating by sticking to the copper electrode and steering the first zinc crystals to lie flat, not by coating the growing zinc. The result offers a concrete design rule for pairing electrolyte additives with electrode substrates in metal batteries.","discovery_kind":"first_principles","skeptic_critique":{"model":"deepseek-v4-flash","headline":"PEO/Zn non-interaction claim is derived from oxidized Zn(OH)2/ZHS surfaces, not metallic Zn under deposition potential; this exclusion is load-bearing for the substrate-only mechanism.","rationale":"The reader's weakest_assumption focused on the computational representation of PEO (DEG for PEO, uniform dielectric film), which is a serious concern. However, I identify the experimentally accessible claim about Zn–PEO non-interaction as the single most load-bearing issue: it is the negative half of the central claim ('rather than by binding to growing Zn crystal surfaces') and the basis for the proposed design principle. The evidence for it is gathered on oxidized surfaces (Zn(OH)2/ZHS), not on metallic Zn under cathodic polarization, so the conclusion does not follow. If PEO does adsorb on growing Zn, the orientation bias could be explained by Zn facet passivation, and the paper's mechanistic novelty would collapse even though the observed smoothing effect remains real. The reader's verdict of CONDITIONAL remains appropriate: the positive experimental evidence (PEO–Cu adsorption by CFFM/PiFM, orientation shift in EC-AFM) is coherent and reproducible, but the mechanistic attribution is not yet established without addressing this gap. My recommendation is therefore UNCHANGED relative to the reader's CONDITIONAL verdict, pending the proposed in-situ test.","tokens_in":24858,"tokens_out":9886,"duration_ms":94501,"concrete_test":"Perform in-situ CFFM adhesion mapping on a Zn electrode in 0.1 M ZnSO4 + 0.1 wt% PEO while holding the deposition potential (e.g., -0.015 V vs Zn), without ever switching off the potential before measurement, and compare to the same surface after the potential is removed and oxidation occurs. If regions with adhesion >1 nN appear on the metallic Zn surface under potential, the premise that PEO does not interact with growing Zn is falsified; if no such regions appear, the exclusion is supported. Complement with in-situ ATR-FTIR under potential monitoring PEO-specific bands near 1462 cm-1.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim requires excluding PEO binding to growing Zn crystals, but the supporting experiments in the section 'Zn oxidation and PEO adsorption on Zn' (Fig. 3, Fig. S18, S19) are performed on Zn foil or electrodeposited Zn after the deposition potential is removed, where the surface spontaneously oxidizes to Zn(OH)2 and Zn4SO4(OH)6·xH2O (ZHS). The authors explicitly state 'no PEO polymer adsorbed onto the Zn surfaces after oxidation' and then conclude 'PEO adsorption does not influence Zn electrodeposition.' This is a non-sequitur: Zn electrodeposition occurs on metallic Zn under a cathodic potential, not on the oxidized, potential-free surface. The paper even acknowledges that PEO adsorption 'cannot outcompete the natural and spontaneous oxidation of the Zn surface,' but that says nothing about adsorption on the actively reducing metal. If PEO adsorbs on metallic Zn under potential, the observed orientation bias could arise from facet-specific Zn–PEO interactions rather than PEO–Cu substrate binding, directly contradicting the proposed design principle of 'minimal interaction with growing crystals.' The reader's rationale flagged this as an overreach, but it is arguably more load-bearing than the computational simplification because it undermines the negative half of the central claim and is cleanly testable experimentally.","agreement_with_reader":"partial"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper investigates the mechanism by which the polymer additive PEO smooths Zn electrodeposition on Cu substrates. Using in-situ electrochemical atomic force microscopy (EC-AFM), the authors report that 0.1 wt% PEO shifts the orientation distribution of Zn platelets from predominantly inclined/vertical to predominantly flat-lying (002)-oriented, changing the stated ratio of (002)-oriented to (101)- and (100)-oriented plates from 1:3 to 3:2, while leaving platelet sizes and aspect ratios similar. Complementary adhesion-force mapping, PiFM, and contact-angle measurements are used to show that PEO adsorbs on Cu but not on oxidized Zn surfaces. DFT calculations, using diethylene glycol (DEG) as a proxy for PEO, predict that PEO reverses the interfacial energy preference from Cu/Zn(100) in water (ΔE = -369.9 kJ/mol) to Cu/Zn(002) in PEO (ΔE = +294.2 kJ/mol), and coupled PNP/cDFT simulations, modeling the polymer as a uniform dielectric film (ε = 2), predict a 0.8 eV Zn2+ potential-of-mean-force barrier that shifts deposition to a diffusion-limited regime. The authors propose a design principle: polymer additives with strong substrate binding but minimal interaction with the growing metal can smooth electrodes by controlling the nucleation orientation.","tokens_in":25086,"tokens_out":6454,"duration_ms":62791,"significance":"The paper addresses a long-standing question in aqueous Zn batteries and provides a novel, testable design principle: substrate-selective polymer adsorption controls the nucleation orientation of electrodeposited metal, rather than the commonly assumed ion-binding or growing-crystal-binding mechanisms. The experimental work is extensive and includes multiple independent probes of PEO adsorption (CFFM, PiFM, contact angle), in-situ EC-AFM observation, and careful controls excluding side reactions, oxygen effects, pH-induced precipitation, and Cu grain-orientation effects. If the central claims are confirmed, the study would be a valuable contribution to understanding and designing dendrite-suppressing additives. However, the central quantitative claim (the 1:3 to 3:2 orientation-ratio shift) is presented without plate counts or error bars; the computational mechanism rests on strong, untested simplifications (DEG for PEO and a uniform ε = 2 film); and the claim that PEO does not interact with growing Zn is inferred exclusively from experiments on oxidized Zn surfaces after potential removal, not on metallic Zn under cathodic potential.","major_comments":[{"comment":"The negative half of the central claim — that 'PEO adsorption does not influence Zn electrodeposition' (final paragraph of this section) — is derived entirely from experiments performed after the deposition potential was removed, where the Zn surface spontaneously oxidizes to Zn(OH)2 or ZHS. The manuscript itself states that 'PEO adsorption on the Zn surface cannot outcompete the natural and spontaneous oxidation of the Zn surface,' but this says nothing about adsorption on metallic Zn under a cathodic potential, where the surface is being actively reduced. The proposed design principle requires that PEO have 'minimal interaction with growing crystals'; if PEO adsorbs on metallic Zn facets under potential, the observed orientation bias could instead arise from facet-specific Zn–PEO interactions rather than PEO–Cu substrate binding. This is a load-bearing point, and it needs to be probed under electrodeposition conditions — for example, by measuring adhesion or mass changes on a Zn electrode held at deposition potential (e.g., EC-AFM-based force mapping on a Zn single crystal or electrochemical quartz crystal microbalance), or by studying PEO adsorption on Zn single-crystal surfaces at controlled potential.","section":"Zn oxidation and PEO adsorption on Zn (Fig. 3, Fig. S18, S19)"},{"comment":"The computational mechanism rests on two strong representational choices: DFT replaces high-molecular-weight PEO with 14 diethylene glycol (DEG) molecules, and cDFT models the adsorbed polymer as a uniform, ion-permeable film with a dielectric constant of 2. The reversal of the interfacial-energy preference (ΔE from -369.9 to +294.2 kJ/mol in Table 1) and the 0.8 eV Zn2+ PMF barrier in Fig. 4c both depend on these choices, yet the paper does not report sensitivity tests to the number of DEG molecules, the polymer conformation, or the film dielectric constant (bulk hydrated PEO has a substantially higher dielectric response than 2). Without such sensitivity analysis, the simulations cannot be said to quantitatively confirm the experimental observations; they should be presented as qualitative support, or the model should be calibrated against a measured property of the adsorbed PEO film (for example, an ellipsometric or capacitive estimate of the film's dielectric constant and thickness).","section":"Mechanism by which PEO biases the nucleation orientations (Table 1, Fig. 4c)"},{"comment":"The central experimental quantitative claim is that the ratio of Zn(002)-oriented to Zn(101)- and Zn(100)-oriented plates 'increases from 1:3 before adding PEO to 3:2 after,' but the paper does not report the number of plates counted, error bars, or the statistical treatment used to assign the <30° vs. >30° tilt threshold across the image series. The histograms in Fig. 1a and 1b lack count labels, so the reader cannot judge the robustness of the orientation shift. Because this orientation-ratio change is the empirical foundation for the entire proposed mechanism, the authors should provide plate counts, per-image statistics, and a reproducibility statement from at least three independent electrodeposition experiments, along with a precise definition of how the 30° threshold maps to the (002), (101), and (100) orientation classes.","section":"Results: Zn electrodeposition on Cu substrates (Fig. 1a, b)"}],"minor_comments":[{"comment":"The sentence 'Thermodynamic preference of certain orientations of the growing particles is not necessarily insufficient to understand the interfacial processes occurring during electrodeposition' contains a double negative and should be rephrased to state the intended logic clearly.","section":"Mechanism by which PEO biases the nucleation orientations"},{"comment":"The 'parallel-to-inclined ratio' mentioned in the abstract and the 'ratio of Zn(002)-oriented to Zn(101)- and Zn(100)-oriented' mentioned in the text are not obviously the same quantity; please define both consistently and explain how the 30° threshold separates the three crystallographic classes.","section":"Abstract and Results"},{"comment":"In the sentence referring to Fig. S22, 'Reducing the diffusion rate by lowering ZnSO4 concentration shifts electrodeposition toward a diffusion-limited process, leading to Zn plates with a bigger parallel-to-inclined ratio,' please clarify whether the same statistical analysis protocol as in Fig. 1 was applied to the lower-concentration data.","section":"Mechanism by which PEO biases the nucleation orientations"},{"comment":"The statement that 'the average adhesion force in 0.1 M ZnSO4 increased by roughly 0.1 nN upon addition of 0.1 wt% PEO' may be below the noise floor of the force-curve measurements; please report the force resolution and the statistical significance of this difference.","section":"Zn oxidation and PEO adsorption on Zn (Fig. 3j)"},{"comment":"The caption states 'The energy per surface atom is 1.2 times lower for (100) orientation than that for (002) plate,' which is ambiguous; please report the actual computed energy values.","section":"Supplementary Fig. S20 caption"}],"recommendation":"major_revision","confidential_remarks":"The reviewer's main reservation is the logical gap in the negative claim: the paper asserts that PEO does not interact with growing Zn crystals based solely on experiments on oxidized Zn surfaces at open circuit. This is a clean, testable issue, and the authors already have the in-situ AFM capability to address it by studying a Zn electrode under cathodic potential. The computational model is a strong simplification, but the authors are transparent about it; sensitivity tests would greatly strengthen the paper. The paper is within the journal's scope and the experimental characterization is extensive. I would support acceptance after major revision, provided the statistics and the negative interaction claim are addressed."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"The thing to know: this paper is worth reading for the in-situ EC-AFM result, but the mechanistic story is only partly proven. The observation that 0.1 wt% PEO shifts the Zn platelet orientation ratio from roughly 1:3 to 3:2 in favor of flat-lying (002) plates on Cu is clear and, as far as I can tell, new. The paper also does a good job ruling out the obvious alternative explanations—dissolved oxygen, pH-driven precipitation, Cu facet selection, Zn–Cu alloying, and Cl− impurities. The CFFM, PiFM, and contact-angle evidence for PEO adsorption on Cu is internally consistent and multi-technique. That is a solid empirical core.\n\nThe soft spot is bigger than the reader's report suggests. The claim that PEO does not interact with growing Zn surfaces is the negative half of the central argument, and it is inferred from experiments on Zn foil or deposited Zn after the deposition potential is removed, where the surface has oxidized to Zn(OH)2 and ZHS. The paper even states that PEO adsorption cannot outcompete Zn surface oxidation. That says nothing about adsorption on metallic Zn under a cathodic potential. So the conclusion \"PEO adsorption does not influence Zn electrodeposition\" does not follow. If PEO does adsorb on metallic Zn under potential, the observed orientation bias could come from facet-specific Zn–PEO interactions rather than substrate-only binding. This is load-bearing for the proposed design principle of \"minimal interaction with growing crystals,\" and it is cleanly testable. A serious revision should either add an in-situ test on Zn under potential or explicitly soften the claim.\n\nTwo other issues, in proportion. The orientation statistics lack plate counts and error bars; the 1:3 vs 3:2 ratio should be quantified properly. The computational support is suggestive, not conclusive: DEG as a proxy for high-MW PEO, a uniform epsilon=2 film in cDFT, LDA at Gamma point, and no sensitivity analysis. I would treat the DFT/cDFT as illustrative rather than decisive.\n\nWho gets value: people working on aqueous zinc batteries, dendrite suppression, and electrodeposition additives. The paper deserves a serious referee, not a desk reject, because the empirical observation is real and the mechanistic question is important. My recommendation: send it to peer review and require the authors to fix the Zn non-interaction claim and add proper error statistics. As is, it is a conditional accept at best.","headline":"The paper has a genuinely visible result—PEO flips Zn platelet orientation on Cu—but it overreaches by asserting PEO does not interact with growing Zn, a claim built on oxidized, potential-free surfaces rather than metallic Zn under deposition conditions.","tokens_in":25725,"tokens_out":2333,"would_cite":false,"duration_ms":25970,"reading_group":"maybe","serious_thinker":"yes","would_accept_peer_review":true},"rs_alignment":null,"lean_confirmation":null,"pith_extraction":{"msc":[],"pacs":[],"model":"deepseek-v4-flash","headline":"This paper claims that PEO, a common polymer additive, smooths zinc electrodeposits on copper by adsorbing on the copper substrate and biasing nucleation toward flat-lying (002)-oriented zinc platelets, not by binding to zinc ions or to…","keywords":["zinc electrodeposition","polyethylene oxide","dendrite suppression","nucleation orientation","electrode smoothing","in-situ atomic force microscopy","density functional theory","aqueous zinc batteries"],"falsifier":"Measure the dielectric constant, thickness, and ion permeability of the PEO layer adsorbed on copper in 0.1 M ZnSO4 using in-situ ellipsometry or neutron reflectometry, then recompute the $\\mathrm{Zn}^{2+}$ potential of mean force with the measured film properties; if the barrier is far below 0.8 eV or the PEO environment no longer stabilizes $\\mathrm{Cu}(111)/\\mathrm{Zn}(002)$ over $\\mathrm{Cu}(111)/\\mathrm{Zn}(100)$, the proposed mechanism is falsified even if PEO still changes the platelet orientation distribution.","tokens_in":24579,"feed_emoji":"🔋","tokens_out":7913,"duration_ms":69396,"temperature":0.7,"pith_summary":"This paper claims that polyethylene oxide (PEO) smooths zinc electrodeposits on copper by acting on the substrate rather than on the growing metal. Using in-situ electrochemical atomic force microscopy, the authors find that PEO shifts the ratio of flat-lying $\\mathrm{Zn}(002)$-oriented plates to inclined and vertical $\\mathrm{Zn}(101)$/$\\mathrm{Zn}(100)$ plates from 1:3 to 3:2, with essentially no change in plate size or growth habit. Density functional theory calculations show that PEO reverses the interfacial energy preference of $\\mathrm{Zn}(100)$ over $\\mathrm{Zn}(002)$ on Cu, and classical DFT simulations predict a $\\sim0.8$ eV barrier to $\\mathrm{Zn}^{2+}$ approaching the PEO-covered electrode, which would confine deposition to a narrow near-surface zone. The paper argues this is the mechanism behind the widely reported but previously unexplained smoothing and dendrite-suppression effect of PEO in aqueous zinc batteries.","feed_headline":"PEO flattens zinc plating by steering crystal nuclei on copper","feed_subtitle":"In-situ AFM shows PEO binds copper, not zinc, lifting flat-lying platelet ratio from 1:3 to 3:2.","key_machinery":"The load-bearing object is the pair of interfaces $\\mathrm{Cu}(111)/\\mathrm{Zn}(002)$ and $\\mathrm{Cu}(111)/\\mathrm{Zn}(100)$ in water versus a PEO-saturated environment; DFT computes their relative interfacial energies and shows the solvent reverses which orientation is stable. The kinetic side is carried by the $\\mathrm{Zn}^{2+}$ potential of mean force from classical DFT, computed with the adsorbed polymer modeled as a uniform, ion-permeable film of dielectric constant 2, which yields a $\\sim0.8$ eV barrier and a depletion zone for $\\mathrm{Zn}^{2+}$ near the electrode. Together these two calculations connect the observed platelet orientation bias to a thermodynamic preference plus a shift from reaction-limited to diffusion-limited electrodeposition.","core_discovery":"The central claim is that PEO does not regulate zinc morphology by adsorbing on zinc crystal faces or by complexing $\\mathrm{Zn}^{2+}$ ions, as earlier studies assumed; it adsorbs selectively on the copper substrate and alters the interfacial energy landscape for nucleation. The experimental evidence shows the first zinc layer determines all subsequent layer-by-layer growth, and that PEO biases this first layer toward $\\mathrm{Zn}(002)$ platelets lying parallel to the substrate. EBSD and SEM show no correlation between zinc plate orientation and the crystallographic orientation of the underlying copper grains, ruling out facet-selective polymer adsorption as the cause. DFT places the energy difference $\\Delta E = E[\\mathrm{Cu}(111)/\\mathrm{Zn}(100)] - E[\\mathrm{Cu}(111)/\\mathrm{Zn}(002)]$ at $-369.9$ kJ/mol in water (favoring vertical $\\mathrm{Zn}(100)$) and $+294.2$ kJ/mol in a PEO (diethylene glycol) environment (favoring flat $\\mathrm{Zn}(002)$). Combined with cDFT simulations of a low-dielectric polymer film that raises the $\\mathrm{Zn}^{2+}$ potential of mean force by about $0.8$ eV, the paper concludes that PEO both thermodynamically stabilizes flat-lying nuclei and kinetically confines deposition to the near-surface region, producing a smooth film by template-controlled Frank–van der Merwe growth.","pith_inferences":["A testable extension would be to measure the dielectric constant and thickness of the adsorbed PEO layer on copper in working electrolyte; if the film is not compact and low-dielectric, the calculated 0.8 eV barrier is an artifact even though the orientation bias could still be real.","The same substrate-binding logic suggests a synthetic target: polymers with ether or other coordinating groups that bind oxidizable current collectors but not the depositing metal may generalize the effect to lithium, sodium, or calcium anodes.","Because the paper models PEO by small diethylene glycol molecules, the claim would be stronger if the energy reversal were reproduced with explicit longer-chain polymer conformations on the Cu surface.","One could also probe the nucleation-bias claim directly by depositing zinc on PEO-patterned copper, where flat platelets should appear preferentially on PEO-covered regions if the mechanism is correct."],"forward_implications":["If the mechanism is right, any polymer that binds the current collector more strongly than the deposited metal should be able to flatten electrodeposits, not just PEO on copper.","The first nucleated layer controls the texture of the whole film, so additives only need to act during nucleation; they can desorb as the metal grows.","The model predicts that raising current density or lowering $\\mathrm{ZnSO}_4$ concentration, which pushes the system toward diffusion-limited deposition, should increase the fraction of flat-lying $\\mathrm{Zn}(002)$ plates.","In aqueous zinc batteries, the smoothing effect of PEO should appear primarily at the early deposition stage on the substrate, not during steady stripping/plating on an established zinc surface.","The proposed design rule could be used to screen polymer additives for other metal-anode chemistries by measuring polymer–substrate adhesion and computing the interfacial energy reversal for the target metal."],"supporting_citations":[{"why":"Reports the earlier finding that PEO improves Zn anode cycling, the unexplained effect this paper sets out to explain.","marker":"[20]"},{"why":"Defines the Frank–van der Merwe layer-by-layer growth mode used to argue the first layer templates the film.","marker":"[32]"},{"why":"Provides the DFT method and software used for the interfacial-energy calculations.","marker":"[53–55]"},{"why":"States that reaction-limited electrodeposition forms thermodynamically stable morphologies, the contrast case for PEO-induced diffusion limitation.","marker":"[56]"},{"why":"Reports that high current density produces planar Zn(002) deposits, cited as independent support for the reaction/diffusion balance.","marker":"[59–61]"},{"why":"Presents the alternative hypothesis of facet-selective ligand adsorption on Cu that the authors test and exclude.","marker":"[15]"}],"fun_headline_variants":["PEO binds copper to steer zinc nucleation flat","Smooth zinc via polymer–copper binding, not zinc binding","PEO's role: substrate binding controls zinc film smoothness","Zinc plating smoothed by polymer that targets the substrate"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"The load-bearing premise is that the computational representation of PEO—small diethylene glycol molecules standing in for the polymer and a uniform low-dielectric film with dielectric constant 2—faithfully captures how real PEO behaves at the copper–electrolyte interface; if real PEO forms a diffuse or high-dielectric layer, the calculated energy reversal and the 0.8 eV kinetic barrier would not apply.","fun_headline_variants_meta":{"raw":{"variants":["PEO binds copper to steer zinc nucleation flat","Smooth zinc via polymer–copper binding, not zinc binding","PEO's role: substrate binding controls zinc film smoothness","Zinc plating smoothed by polymer that targets the substrate"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000278,"raw_usage":{"total_tokens":1728,"prompt_tokens":1094,"completion_tokens":634,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":710,"completion_tokens_details":{"reasoning_tokens":567}},"tokens_in":710,"tokens_out":634,"duration_ms":6771,"temperature":1.0,"reasoning_tokens":567,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-08T17:51:29.342230+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure the dielectric constant, thickness, and ion permeability of the PEO layer adsorbed on copper in 0.1 M ZnSO4 using in-situ ellipsometry or neutron reflectometry, then recompute the $\\mathrm{Zn}^{2+}$ potential of mean force with the measured film properties; if the barrier is far below 0.8 eV or the PEO environment no longer stabilizes $\\mathrm{Cu}(111)/\\mathrm{Zn}(002)$ over $\\mathrm{Cu}(111)/\\mathrm{Zn}(100)$, the proposed mechanism is falsified even if PEO still changes the platelet orientation distribution.","supporting_citations":[{"cited_title":"#), electrostatic correlations (𝐹","cited_arxiv_id":null,"evidence_quote":"Defines the Frank–van der Merwe layer-by-layer growth mode used to argue the first layer templates the film."}],"review_version":1}