A method, comprising: determining a hydrogen leak rate in a polymer electrolyte membrane fuel cell stack, the determining including: generating a first set of data points for impedance signatures of oxygen concentrations in a first fuel cell test stack, the first fuel cell test stack having no internally leaky cells; and generating a second set of data points for impedance signatures of differential pressures of hydrogen and oxygen in a second fuel cell test stack, the second fuel cell test stack having at least one internally leaky cell; mapping the impedance signatures of the oxygen concentrations from the first set of data points to the impedance signatures of the differential pressures of hydrogen and oxygen from the second set of data points; passing an AC signal through the fuel cell stack; detecting impedance signatures from the AC signal in the fuel cell stack; identifying an oxygen concentration of the fuel cell stack by matching the impedance signature from the AC signal with the impedance signature of the oxygen concentration in the first fuel cell test stack; and calculating the hydrogen leak rate of the fuel cell stack by matching the oxygen concentration of the fuel cell stack with the impedance signature of the differential pressure of the second fuel cell test stack. determining a hydrogen leak rate in a polymer electrolyte membrane fuel cell stack, the determining including: generating a first set of data points for impedance signatures of oxygen concentrations in a first fuel cell test stack, the first fuel cell test stack having no internally leaky cells; and generating a second set of data points for impedance signatures of differential pressures of hydrogen and oxygen in a second fuel cell test stack, the second fuel cell test stack having at least one internally leaky cell; mapping the impedance signatures of the oxygen concentrations from the first set of data points to the impedance signatures of the differential pressures of hydrogen and oxygen from the second set of data points; passing an AC signal through the fuel cell stack; detecting impedance signatures from the AC signal in the fuel cell stack; identifying an oxygen concentration of the fuel cell stack by matching the impedance signature from the AC signal with the impedance signature of the oxygen concentration in the first fuel cell test stack; and calculating the hydrogen leak rate of the fuel cell stack by matching the oxygen concentration of the fuel cell stack with the impedance signature of the differential pressure of the second fuel cell test stack. generating a first set of data points for impedance signatures of oxygen concentrations in a first fuel cell test stack, the first fuel cell test stack having no internally leaky cells; and generating a second set of data points for impedance signatures of differential pressures of hydrogen and oxygen in a second fuel cell test stack, the second fuel cell test stack having at least one internally leaky cell; mapping the impedance signatures of the oxygen concentrations from the first set of data points to the impedance signatures of the differential pressures of hydrogen and oxygen from the second set of data points; passing an AC signal through the fuel cell stack; detecting impedance signatures from the AC signal in the fuel cell stack; identifying an oxygen concentration of the fuel cell stack by matching the impedance signature from the AC signal with the impedance signature of the oxygen concentration in the first fuel cell test stack; and calculating the hydrogen leak rate of the fuel cell stack by matching the oxygen concentration of the fuel cell stack with the impedance signature of the differential pressure of the second fuel cell test stack.