Methodology

The concentrations of Fe, Ag, Pb, Ni, and Pd were quantified on Friday, December 1st 2023 with the aid of an Agilent 7500ce ICPMS housed within the Jackson School of Geological Sciences, at the University of Texas at Austin. The CeO/Ce ratio was evaluated to be <1.05% which is a good indication that plasma temperature is optimized for its sensitivity and that the plasma is optimal enough to break down polyatomic interferences such as plasma-based oxides. Polyatomic interferences were eliminated by operating the octupole reaction system in helium and hydrogen mode. Further quality control measures such as the use of internal standards to check for instrumental drift were applied and the results indicate that the internal standard sensitivity was within the quality assurance tolerance range (60-160%).
Table X. ICP-MS operating conditions and instrument parameters

Research Objectives

The goal of this study is to develop a method that can accurately quantify the concentration of metallic impurities (Ni and Fe) present in the electrolytes in periodic electrochemical cycling. The objectives can be narrowed down to:

To evaluate the concentration of Ni, and Fe in different electrolytes before and after each electrochemical cycling
To evaluate the Pd content leached into the aminoboration reaction mixture
Determination of analytical figures of merits such as LOD, LOQ, and LOL for each analyte
Optimization of instrumental conditions for aforementioned metal determination
Evaluating the precision and accuracy of the method

Electrolyte Samples

The sample set for this is 1M KOH which is of two types: Fe-free KOH and Unpurified KOH (Fe-containing KOH).

The 1M unpurified KOH is prepared by weighing 62.3396 grams of 90 % purity KOH and dissolving in 1L solution.
Also, 1M Fe-purified sample is prepared by following an established protocol ³⁴
Next, the total dissolved solids (TDS) content of the samples are evaluated from the mass concentration of 1M KOH to check if the sample is safe to run on the instrument (TDS ≤ 200 mg/L)
The concentration of Ni, Fe, Ag, and Pb in the samples are checked pre- and post-HER using solution mode ICPMS protocol.
As a control, Fe-purified KOH is prepared and analyzed for its Fe content pre- and post-electrochemical reaction.

Interferences

In the table below we have listed all possible interferences with our analytes of interest for the electrolyte and the aminoboration samples.

Table 1: List of analytes and possible polyatomic ion interferences

Isotopes	Relative Abundance (%)	Possible Interferences
⁶⁰Ni	26.223	³⁶Ar²⁴Mg, ⁴⁴Ca16O, ⁴³Ca¹⁶OH, ⁴²Ca¹⁸O, ⁴³Ca¹⁷O, ⁴⁴Ca¹⁶O, ⁴²Ca¹⁷O¹H
⁵⁶Fe	91.72	⁴⁰Ar¹⁶O, ³⁸Ar¹⁸O, ⁴⁰Ar¹⁵NH,³⁸Ar¹⁷OH, ³⁹K¹⁷O, ⁴⁰K¹⁶O, ³⁷Cl¹⁸OH
²⁰⁸Pb	52.4	⁹²Pt¹⁶O, ¹⁹¹Ir¹⁷O, ¹⁹⁰Pt¹⁸O
¹⁰⁷Ag	51.84	³⁶Ar₂¹⁷O¹⁸O, ³⁶Ar³⁸Ar¹⁶O¹⁷O, ⁹¹Zr¹⁶O, ⁸⁹Y¹⁸O, ⁹⁰Zr¹⁷O, ²⁸Si⁷⁹Br, ²⁶Mg⁸¹Br
¹⁰⁹Ag	48.16	³⁸Ar₂¹⁶O¹⁷O, ³⁶Ar³⁸Ar¹⁷O¹⁸O, ³⁶Ar⁴⁰Ar¹⁶O¹⁷O, ⁹²Zr¹⁶OH, ⁹¹Zr¹⁸O, ⁹²Zr¹⁷O, ⁹²Mo¹⁷O, ⁸Si⁸¹Br, ³⁰Si⁷⁹Br
¹⁰⁵Pd	22.33%	⁶⁵Cu⁴⁰Ar⁺, ⁸⁹Y¹⁶O⁺, ⁸⁸Sr¹⁷O⁺, ⁸⁸Sr¹⁶O¹H⁺, ⁸⁷Sr¹⁸O⁺, ⁶⁸Zn³⁷Cl⁺, and ⁷⁰Zn³⁵Cl⁺

Instrumental Conditions

Plasma Tuning & Instrument Optimization

Plasma tuning and instrument optimization will be done based on the work by Landing and co-workers and will be modified as needed with other literature cited in the background.

Method Quality

The method quality will be assessed based on

1. The percentage recoveries 2. The coefficient of determination 3. Limit of detection 4. Low Relative standard deviation from the results.

Calibration Curves

To evaluate the samples, an analytical protocol based on the work by Landing and co-workers will be modified as needed with other literature cited in the background.

Analytical Sequence

Calibration
Method Blank
Matrix Blank
QC Standards
Unknowns

Budget and Time Frame

The samples obtained for this study are all liquids and consequently will be analyzed using solution mode ICPMS. We project to analyze about ~25 samples and at a unit cost of $17 per solution will total $425.

Blanks

2% nitric acid for Purified KOH electrolyte samples.
2% nitric acid for Organic mixture electrolytes.

Calibration standards

The calibration curves are generated using ICP-MS grade multi-element calibration standards. The linear dynamic range for the analysis runs from 0.5-1000 ppb for Ni, Fe, Pb, Ag, and Pd.

Quality controls

Three sets of quality control samples for purified and unpurified electrolyte

QC1: 82.18 ppb Ni, 410.60 ppb Fe, 82.18 ppb Ag, and 81.69 ppb Pb
QC2: 162.55 ppb Ni, 812.20 ppb Fe, 162.47 ppb Ag, 161.58 ppb Pb, and 20.04 ppb Pd

Samples

Electrolyte samples

Unpurified (Fe-containing) 1 M KOH (1)
Purified (Fe-free) 1 M KOH (1)
Fe-purified electrolyte samples (8)
Fe-containing electrolyte samples (8)

Aminoboration Samples

The aminoboration reactions with Pd/Al₂O₃ will be set up generally as indicated in Table S22 of Ref. 13 with the following changes:

No reactions with ⁿBu₄NCl
The following x mol%:
- 50 mol% Fe(OTf)₃
- 50 mol% Cu(OTf)₂
- 50 mol% Zn(OTf)₂
- 10 mol% benzoquinone (BQ)
- 0 mol% additive

The general reaction workup for ICP-MS analysis is as outlined in SI section 5.10, consisting of centrifugation of solid and supernatant, then aqua regia digestion in microcentrifuge tubes. While microwave digestion has also been employed for analysis of palladium in solution via ICP-MS^15,18,19, aqua regia digestion/centrifugation will be employed as 1) a convenient way in which to separate and analyze Pd content in both supernatant and solid phase and 2) to maintain consistency with previous method parameters. Analysis of the product will similarly be obtained via GC-FID using the internal standard 1-methyl naphthalene. ICP-MS data will be compared to standard solutions of common interferences and analytes, and calibration curves for quantification.

The analysis will be conducted primarily for the isotopically most abundant ¹⁰⁵Pd within the solution, and rinse samples will consist of 2% nitric acid solution. Notably, no common isobaric or doubly charged ion interferences have been listed for this isotope, but common interferences for this and other Pd isotopes are outlined in the interference table.¹⁹

Two samples for the reaction with each Lewis acidic additive will be analyzed, corresponding to digested precipitate and supernatant, respectively.

Digested supernatant and digested precipitate using 50 mol % Fe(OTf)₃
Digested supernatant and digested precipitate using 50 mol % Cu(OTf)₂
Digested supernatant and digested precipitate using 50 mol % Zn(OTf)₂
Digested supernatant and digested precipitate using 10 mol % BQ
Digested supernatant and digested precipitate using no additive

Expectations

We anticipate that for the electrolyte samples, there could be an increase in the Ni content due to the incorporation of metallic impurities such as Fe, Pb, and Ag which induces the leaching of Ni. Our focus is to see the impact of Fe and hence we expect a decrease in the concentration of Fe, after each potential cycling. The decrease in concentration of metallic impurities will be contingent on the ionic radius of the metals similar to that of Ni. This result will enable us to know whether any of the metallic impurities are being absorbed into the catalyst and if they are improving or decreasing the electrocatalytic production of hydrogen.

For the aminoboration reaction mixture, it is expected that the iron additive will outperform other additive species, particularly that of the redox-inactive Zn(OTf)₂ and the pure oxidant BQ. Comparison of the previous Fe(OTf)₂to Fe(OTf)₃ may show a greater leaching efficiency as we postulate that Fe^III generated throughout the catalytic cycle serves to re-oxidize these Pd NPs. While Cu(OTf)₂ affords similar norbornene product in the optimized reaction conditions, it may be a poorer leaching agent, therefore potentially also leading to lower yields when using solid-supported Pd/Al₂O₃ as the pre-catalyst Pd source.