{"id":"91e10186-3512-41ce-a4e3-a764fa921447","arxiv_id":"1908.06778","paper_version":1,"verdict":"CONDITIONAL","confidence":"MODERATE","novelty_score":6.0,"correctness_risk":"medium","formal_verification":"none","parameter_count":2,"one_line_summary":"A computer-evolved formula using ionic radius ratios predicts perovskite oxygen evolution activity and guided synthesis of five new catalysts, four of which beat the reference BSCF in same-lab tests.","lead":"The paper uses symbolic regression on 18 measured perovskite catalysts to find a simple formula, VRHE = 1.612 μ/t + 1.073, that predicts oxygen evolution activity from ionic radii. A generalist should read it because it demonstrates a cheap structural descriptor that could replace expensive DFT-based descriptors in electrocatalyst screening.","discovery_kind":"new_application","skeptic_critique":{"model":"deepseek-v4-flash","headline":"BET normalization is the load-bearing assumption: if it does not yield intrinsic activity, the linear μ/t descriptor and the claim that four new catalysts beat BSCF both inherit an arbitrary distortion.","rationale":"The reader's weakest assumption identifies BET normalization as the insecure link. I agree: the entire fitting set and the new-catalyst comparison depend on the same normalization, and the Suntivich external check uses the same BET procedure, so it cannot independently validate the intrinsic scale. The concern is load-bearing because if BET area over/underestimates the active area differently for the new catalysts relative to BSCF, both the linear descriptor fit (trained on BET-normalized labels) and the headline 'four outperform BSCF' could be distorted. The paper's own data show overlapping error bars between BSCF and the new catalysts (e.g., BSCF 1.614–1.663 vs SrNi0.75Co0.25O3 1.605–1.635), so even on the reported scale the improvement is not clearly significant; the normalization assumption is what stands between the averages and a robust claim. Because the reader already conditioned the verdict, no adjustment is needed.","tokens_in":14848,"tokens_out":7953,"duration_ms":77514,"concrete_test":"Measure the BET surface area and the double-layer capacitance (ECSA) of BSCF and of the four new catalysts (Cs0.4La0.6Mn0.25Co0.75O3, Cs0.3La0.7NiO3, SrNi0.75Co0.25O3, Sr0.25Ba0.75NiO3), then recompute VRHE at a constant ECSA-normalized current density (e.g., 10 mA cm−2 ECSA) and also at constant 5 mA cm−2 disk current without any BET normalization. If the four new catalysts no longer have lower VRHE than BSCF in both alternative analyses, the claimed outperformance is an artifact of the BET normalization.","verdict_should_be":"UNCHANGED","load_bearing_attack":"The central claim (VRHE = 1.612μ/t + 1.073, lower μ/t = better) rests on a set of VRHE values measured at 5 mA cm−2 disk current and normalized by loading and BET surface area (Methods; Fig. 2c caption). This normalization assumes the entire BET area is electrochemically active and that the normalized current density (10 mA cm−2 oxide for BSCF) is a fair common metric. No BET values are reported for the new perovskites, so the comparison of the four new catalysts against BSCF at constant normalized current could be biased: if the new materials have higher or lower BET area, the disk current density at which VRHE is read differs, and capacitive or resistance artifacts (only 98% iR compensation) could enter. The external Suntivich validation (Fig. S3b) does not rescue the claim, because Suntivich et al. also normalized by BET surface area, so it inherits the same assumption. Without evidence that BET area equals electrochemically active surface area (or that the ranking is robust to alternative normalizations), the descriptor and the outperformance claim are not on a secure intrinsic scale.","agreement_with_reader":"agree"},"referee_report":{"model":"deepseek-v4-flash","summary":"The paper uses symbolic regression on a newly measured, self-consistent dataset of 18 known oxide perovskite OER catalysts to derive an analytical descriptor for the oxygen evolution reaction overpotential. The selected two-parameter formula, VRHE = 1.612 μ/t + 1.073, where μ is the octahedral factor and t the tolerance factor, is used to screen 3,545 charge-balanced perovskite compositions. Thirteen low-μ/t candidates were chosen for synthesis; five formed phase-pure perovskites, and four of these are reported to have lower VRHE at a common normalized current density than Ba0.5Sr0.5Co0.8Fe0.2O3 (BSCF), the literature benchmark. The descriptor is also tested against independent measurements by Suntivich et al., showing a linear correlation with comparable mean absolute error.","tokens_in":15131,"tokens_out":5889,"duration_ms":61068,"significance":"If the descriptor is robust, the paper makes a useful contribution: an interpretable, parameter-light formula linking perovskite structural factors to OER activity, with a complete workflow from regression to experimental verification. The self-consistent dataset and the external comparison with Suntivich et al. are concrete strengths, as is the explicit screening of 3,545 compositions. The claim that four new perovskites outperform BSCF is potentially impactful and would be a strong demonstration of data-driven discovery. However, the validation currently rests on a normalization assumption and on mean values whose uncertainty intervals overlap with BSCF, so the significance of the central discovery claim is not yet established to the standard the paper aims for.","major_comments":[{"comment":"The comparison of new catalysts with BSCF is made at a fixed normalized current density (10 mA cm−2 oxide), which is obtained by dividing the disk current density by the product of catalyst loading and BET surface area. The paper reports the BET area for BSCF (0.30 m2 g−1) and states that 10 mA cm−2 oxide corresponds to 5.0 mA cm−2 disk current for BSCF, but it does not report BET areas for any of the five new perovskites. If the new materials have different BET areas, the disk current densities at which VRHE is read differ, so the measured potentials may not be directly comparable. The Suntivich validation inherits the same BET normalization and therefore does not independently resolve this issue. Please report the BET areas for all new catalysts and demonstrate that the ranking is robust to alternative normalizations (for example, geometric current density or mass activity).","section":"Methods, Table 1, Fig. 2c"},{"comment":"The reported ranges of VRHE for BSCF (1.614–1.663 V) and for the four new catalysts (e.g., Cs0.4La0.6Mn0.25Co0.75O3: 1.562–1.623 V) overlap substantially. Since the central claim is that these new catalysts outperform BSCF, the average differences (16–46 mV) are not clearly separated given the stated experimental uncertainty. The paper should provide a statistical comparison, such as confidence intervals or a t-test, to show that the differences are significant beyond measurement noise. As presented, the claim of outperformance is not fully supported by the data.","section":"Table 1, Fig. 3"},{"comment":"Eight of the thirteen predicted compositions formed significant impurity phases and were excluded from electrochemical testing, leaving only the five phase-pure compounds as the validation set. This selection, together with the small number of new catalysts, weakens the evidence that the descriptor-guided screening identifies active materials with a reasonable success rate. The paper should report the fate of all thirteen candidates (including the eight impure ones) and discuss how the 5/13 success rate affects the claimed discovery capability of the descriptor.","section":"Results (synthesis of new perovskites)"}],"minor_comments":[{"comment":"There are several typos: 'unprecedente dly' in the abstract, 'Colledge' in the affiliation block, and 'Suntvich' in the main text. These should be corrected.","section":"Abstract and affiliations"},{"comment":"The caption says 'The inset Figure are from Ref. [6] with permissions.' The grammar should be fixed, and the figure should indicate whether the inset is reproduced unchanged or reformatted.","section":"Fig. 2c caption"},{"comment":"The description of the hyperparameter grid search states that 43,200,000 analytical formulas were produced (432 parameter sets × 20 generations × 5,000 individuals). This is correct, but the text should clarify that the 8,640 individuals on the Pareto front are the per-generation best fits, not the full population.","section":"Table S3 and Results"},{"comment":"The paper describes the Suntivich comparison as confirmation of 'generality.' Since the same seven compositions appear in the training dataset, the Suntivich data are independent measurements but not out-of-sample for new compositions; the comparison would be more accurately described as a cross-laboratory reproducibility check for known materials.","section":"Discussion of Suntivich validation"},{"comment":"The units of VRHE are reported as V in the table header and text, but the descriptor formula and some figure labels use eV. The potential axis is labeled in V versus RHE, so the constants in the formula (1.612 and 1.073) should be stated as having units of V, not eV, to avoid confusion.","section":"Table 1"}],"recommendation":"major_revision","confidential_remarks":"The stress-test concern about BET normalization is real and should be addressed with explicit data. The overlapping error bars in Table 1 are, in my view, the more serious quantitative issue: the 'outperform BSCF' claim rests on differences that may not be statistically significant. The external Suntivich validation is a genuine strength and partially cushions the circularity concern, but it does not test predictions for new compositions. The paper is within scope for the journal and the central idea is defensible, so I recommend major revision rather than rejection."},"author_rebuttal":null,"desk_editor":{"model":"deepseek-v4-flash","letter":"Colleague,\n\nYou should know two things about this paper. First, it finds a genuinely new descriptor, μ/t (octahedral factor over tolerance factor), that linearly predicts OER activity of oxide perovskites with a MAE around 21 meV on the authors' own data and, more importantly, on Suntivich's independent dataset. Second, the authors use this descriptor to screen over three thousand compositions, synthesize five new perovskites, and report four that outperform BSCF. If the descriptor generalizes, that is a cheap, DFT-free screen worth having.\n\nThe symbolic regression methodology is used competently. The training set is small but self-consistent, and the external validation is real out-of-sample evidence, not just a holdout from the same lab. The physical interpretation—large A-site cations and small B-site cations improve activity—is plausible and consistent with the descriptor.\n\nThe soft spots are in the experimental validation. The central assumption is that normalizing current by loading and BET surface area yields an intrinsic activity scale. That is a big assumption. The paper does not report BET areas for the new catalysts, so we cannot check whether the comparison against BSCF is fair on a common scale. If the new materials have lower BET areas, they would look better at the same normalized current than they are intrinsically. The external Suntivich validation inherits the same normalization, so it does not rescue the intrinsic-activity claim. That said, this normalization is standard in the electrocatalysis literature, so the claim is at least measured on a metric the field accepts.\n\nThe outperformance claim is also not as clean as the abstract suggests. The average VRHE values for the four new catalysts are 18–46 meV lower than BSCF, but the reported ranges overlap with BSCF's range for all four. The best new catalyst shows a 67 meV deviation from its predicted value, which is three times the training MAE. And eight of the thirteen attempted compositions failed to form pure perovskite; only the five pure ones were characterized. That is not a fatal flaw, but it tempers the discovery narrative.\n\nOverall, this is a useful paper for people working on perovskite OER catalysts or materials informatics. It is not a breakthrough, but it is a solid contribution with a new descriptor and honest (if incomplete) experimental support. It deserves a serious referee, not a desk reject. I would recommend sending it to review, but the reviewers should push for BET data on the new catalysts and a discussion of the normalization assumption, and probably a fixed-disk-current comparison as a robustness check.\n\nBest.","headline":"New μ/t descriptor for OER perovskites is genuinely useful and supported by out-of-sample data, but the BET normalization assumption and thin experimental validation make the outperformance claim shakier than the authors let on.","tokens_in":15635,"tokens_out":4577,"would_cite":true,"duration_ms":43407,"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":"A single ratio of two geometric factors, μ/t, quantitatively predicts the oxygen-evolution activity of oxide perovskites and guided the discovery of four new catalysts that beat the current benchmark.","keywords":["symbolic regression","oxygen evolution reaction","oxide perovskites","electrocatalysis","descriptor","tolerance factor","octahedral factor","high-throughput screening"],"falsifier":"Measure OER activity on epitaxial thin films of several perovskites spanning the μ/t range, with identical thickness, orientation, and roughness so loading and BET normalization are unnecessary; if the μ/t versus overpotential slope departs markedly from 1.612 eV per unit μ/t, the reported correlation is an artifact of powder-film normalization rather than an intrinsic property.","tokens_in":14679,"feed_emoji":"⚡","tokens_out":7779,"duration_ms":79475,"temperature":0.7,"pith_summary":"The paper argues that symbolic regression, applied to a self-consistent set of eighteen measured oxide perovskite catalysts, can distill oxygen-evolution activity into an analytical formula: VRHE = 1.612 μ/t + 1.073 eV, where μ is the octahedral factor and t is the tolerance factor. If true, this replaces expensive electronic-structure descriptors with a two-parameter geometric rule computed from tabulated ionic radii. The paper used the rule to screen 3,545 charge-balanced perovskite compositions, synthesized five new ones, and reports that four, including Sr0.25Ba0.75NiO3, show lower overpotential at 5 mA cm−2 than the benchmark catalyst BSCF. The same μ/t line also tracks an independent literature dataset with accuracy comparable to the established eg volcano. A sympathetic reader would take the paper's core claim to be that OER activity in oxide perovskites is essentially a structural-geometry problem, capturable by one ratio.","feed_headline":"One ratio of ionic radii finds perovskites that beat BSCF","feed_subtitle":"Symbolic regression distilled oxygen-evolution activity into μ/t, and four new catalysts outperformed the benchmark.","key_machinery":"The load-bearing object is the ratio μ/t, where μ = rB/rO is the octahedral factor (B-site cation radius over oxygen radius) and t = (rA + rO)/(√2(rB + rO)) is the tolerance factor, a geometric measure of how well A, B, and O ions pack into the perovskite lattice. The descriptor enters through the fitted equation VRHE = 1.612 μ/t + 1.073 eV, chosen from the Pareto front after symbolic regression searched roughly 43.2 million analytical formulas built from simple operators (+, −, ×, ÷, √) and physically motivated terminals. Its work in the argument is to turn OER activity into a quantity computable from ionic radii and charge balance alone, and to supply a monotonic design rule, decrease μ and increase t, that replaces the non-monotonic volcano relationship. The paper also uses μ/t together with perovskite stability criteria to justify screening A-site cations from K, Rb, Cs and B-site cations from 3d transition metals.","core_discovery":"The central discovery claim is the descriptor: the overpotential versus the reversible hydrogen electrode at 5 mA cm−2 disk current, normalized by loading and BET surface area, is linear in μ/t for oxide perovskites, VRHE = 1.612 μ/t + 1.073 eV, with MAE 21.6 meV on the eighteen training compounds. Lower μ/t means higher activity. Because μ = rB/rO and t = (rA + rO)/(√2(rB + rO)), the formula says that larger A-site cations and smaller B-site cations, or higher B-site valence, which shrinks rB, should improve OER activity. The paper reports that all nine Pareto-front formulas from the symbolic regression agree on this qualitative direction, and that the μ/t line reproduces the trend of independently reported data with Pearson correlation 0.928, comparable to the eg descriptor's 0.923. Newly synthesized perovskites with low μ/t, including Cs0.4La0.6Mn0.25Co0.75O3, Cs0.3La0.7NiO3, SrNi0.75Co0.25O3, and Sr0.25Ba0.75NiO3, had measured VRHE below BSCF and close to the predicted values.","pith_inferences":["If the descriptor is right, the practical discovery frontier is synthesizability, not electronic structure: activity should keep rising as μ/t falls until the perovskite structure stops forming, and the paper's failed Cs-rich syntheses mark that empirical boundary.","A natural testable extension is to apply the same μ/t screening to double perovskites and Ruddlesden–Popper phases, where the same geometric variables are defined but the paper does not claim coverage.","The μ/t rule implies that A-site substitution with even larger monovalent cations should further improve activity; a systematic mapping of the synthesis-stability boundary would turn the descriptor into a complete design map.","Because μ/t is purely geometric, the descriptor may also be useful for other perovskite electrocatalytic reactions, though that extension is not established by the paper."],"forward_implications":["Researchers can screen thousands of hypothetical perovskite compositions for OER activity using only tabulated ionic radii and charge balance, with no DFT calculations.","The descriptor supplies a concrete design rule: put large cations on the A site and small 3d transition-metal cations on the B site, or raise the B-site valence to shrink its radius.","Four newly synthesized perovskites, especially Sr0.25Ba0.75NiO3, are claimed to exceed BSCF in both activity and stability under galvanostatic testing.","The linear, monotonic form of the relationship means predicted activity improves continuously as μ/t decreases, unlike the volcano-shaped curves of earlier descriptors.","The same formula reproduces an independent literature dataset with correlation comparable to the established eg descriptor, supporting generality beyond the authors' own measurements."],"supporting_citations":[{"why":"Supplies the symbolic-regression-in-materials-science method the paper builds on.","marker":"[1]"},{"why":"Early perovskite OER descriptor whose parameters motivate the terminal set.","marker":"[3]"},{"why":"Conventional volcano descriptor for OER that the SR formula must match or beat.","marker":"[4]"},{"why":"Independent experimental OER dataset used to verify the μ/t trend and source of the BSCF benchmark.","marker":"[6]"},{"why":"Review of oxide perovskite OER catalysts that frames the design space and prior half-century of data.","marker":"[9]"},{"why":"Defines the tolerance factor t that enters the descriptor.","marker":"[18]"},{"why":"Connects t and μ to cubic perovskite stability, used to justify screening ranges.","marker":"[19]"}],"fun_headline_variants":["μ/t descriptor uncovers perovskites that beat BSCF","Four new perovskites beat BSCF via μ/t ratio","Symbolic regression finds simple descriptor for better OER catalysts","μ/t predicts OER activity: four new perovskites outperform BSCF","New perovskites beat benchmark via simple μ/t rule"],"cache_read_input_tokens":3200,"weakest_assumption_plain":"Everything rests on the assumption that the measured overpotentials, normalized by catalyst loading and BET surface area, put all eighteen training perovskites on a common intrinsic activity scale; if film conductivity, surface reconstruction, or different rate-determining steps break that comparability, the fitted descriptor and all screening predictions inherit the distortion.","fun_headline_variants_meta":{"raw":{"variants":["μ/t descriptor uncovers perovskites that beat BSCF","Four new perovskites beat BSCF via μ/t ratio","Symbolic regression finds simple descriptor for better OER catalysts","μ/t predicts OER activity: four new perovskites outperform BSCF","New perovskites beat benchmark via simple μ/t rule"]},"model":"deepseek-v4-flash","effort":"low","cost_usd":0.000641,"raw_usage":{"total_tokens":2987,"prompt_tokens":1018,"completion_tokens":1969,"prompt_tokens_details":{"cached_tokens":384},"prompt_cache_hit_tokens":384,"prompt_cache_miss_tokens":634,"completion_tokens_details":{"reasoning_tokens":1883}},"tokens_in":634,"tokens_out":1969,"duration_ms":13178,"temperature":1.0,"reasoning_tokens":1883,"cache_read_input_tokens":384,"cache_creation_input_tokens":0},"cache_creation_input_tokens":0},"created_at":"2026-08-14T12:35:10.850772+00:00","model_set":{"reader":"deepseek-v4-flash"},"falsifier":"Measure OER activity on epitaxial thin films of several perovskites spanning the μ/t range, with identical thickness, orientation, and roughness so loading and BET normalization are unnecessary; if the μ/t versus overpotential slope departs markedly from 1.612 eV per unit μ/t, the reported correlation is an artifact of powder-film normalization rather than an intrinsic property.","supporting_citations":[{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Early perovskite OER descriptor whose parameters motivate the terminal set."},{"cited_title":"Science 261, 872-878 (1993)","cited_arxiv_id":null,"evidence_quote":"Conventional volcano descriptor for OER that the SR formula must match or beat."},{"cited_title":null,"cited_arxiv_id":null,"evidence_quote":"Independent experimental OER dataset used to verify the μ/t trend and source of the BSCF benchmark."}],"review_version":1}